I am finally finished with my preliminary survey: I took what you sent as a strawman, and inserted what I found (I tried to say only something about ambiguous naming):

 - The unit of storage in GIT is called "object"; no other word
   is used and the word "object" is used only for this purpose
   so this one is OK.

 - A 20-byte SHA1 to uniquely identify "objects"; README and
   early Linus messages call this "object name" so does
   tutorial.  Many places say "object SHA1" or just "SHA1".

"Object" is short for "immutable object". git-cat-file.txt says
"repository object".

 - An "object database" stores a set of "objects", and an
   individial object can be retrieved by giving it its object

Tutorial calls it an "object store". git-fsck-cache.txt names it
"database" at first, but then also uses "object pool".

 - Storing a regular file or a symlink in the object database
   results in a "blob object" created.  You cannot directly
   store filesystem directory, but a collection of blob objects
   and other tree objects can be recorded as a "tree object"
   which corresponds to this notion.

 - $GIT_INDEX_FILE is "index file", which is a collection of
   "cache entries".  The former is sometimes called "cache
   file", the latter just "cache".

Tutorial says "cache" aka "index". Though technically, a cache
is the index file _plus_ the related objects in the object database.
git-update-cache.txt even makes the difference between the "index"
and the "directory cache".

 - the directory which corresponds to the top of the hierarchy
   described in the index file; I've seen words like "working
   tree", "working directory", "work tree" used.

The tutorial initially says "working tree", but then "working
directory". Usually, a directory does not include its
subdirectories, though. git-apply-patch-script.txt, git-apply.txt,
git-hash-object.txt, git-read-tree.txt
use "work tree". git-checkout-cache.txt, git-commit-tree.txt,
git-diff-cache.txt, git-ls-tree.txt, git-update-cache.txt contain
"working directory". git-diff-files.txt talks about a "working tree".

 - When the stat information a cache entry records matches what
   is in the work tree, the entry is called "clean" or
   "up-to-date".  The opposite is "dirty" or "not up-to-date".

 - An index file can be in "merged" or "unmerged" state.  The
   former is when it does not have anything but stage 0 entries,
   the latter otherwise.

That seems to be unambiguous (sometimes it's called "index",
sometimes "index file"; I don't think that matters).

 - An merged index file can be written as a "tree object", which
   is technically a set of interconnected tree objects but we
   equate it with the toplevel tree object with this set.

 - A "tree object" can be recorded as a part of a "commit
   object".  The tree object is said to be "associated with" the
   commit object.

In diffcore.txt, "changeset" is used in place of "commit".

 - A "tag object" can be recorded as a pointer to another object
   of any type. The act of following the pointer a tag object
   holds (this can go recursively) until we get to a non-tag
   object is sometimes called "resolving the tag".

 - The following objects are collectively called "tree-ish": a
   tree object, a commit object, a tag object that resolves to
   either a commit or a tree object, and can be given to
   commands that expect to work on a tree object.

We could call this category an "ent".

 - The files under $GIT_DIR/refs record object names, and are
   called "refs".  What is under refs/heads/ are called "heads",
   refs/tags/ "tags".  Typically, they are either object names
   of commit objects or tag objects that resolve to commit
   objects, but a tag can point at any object.

The tutorial never calls them "refs", but instead "references".

 - A "head" is always an object name of a commit, and marks the
   latest commit in one line of development.  A line of
   development is often called a "branch".  We sometimes use the
   word "branch head" to stress the fact that we are talking
   about a single commit that is the latest one in a "branch".

In the tutorial, the latter is used in reverse: it talks about a
"HEAD development branch" and a "HEAD branch".

I find it a little bit troublesome that $GIT_DIR/branches does not
really refer to a branch, but rather to a (possibly remote) repository.

 - Combining the states from more than one lines of developments
   is called "merging" and typically done between two branch
   heads.  This is called "resolving" in the tutorial and there
   is git-resolve-script command for it.

 - A set of "refs" with the set of objects reachable from them
   constitute a "repository".  Although currently there is no
   provision for a repository to say that its objects are stored
   in this and that object database, multiple repositories can
   share the same object database, and there is not a conceptual
   limit that a repository must retrive its objects from a
   single object database.

This is referred to as "git archive" in the tutorial at first,
and later as "repository". However, in "Copying archives", a
very confusing explanation tells us that a "repository" normally
is a "working tree", where I would rather say that the repository
lives inside a hidden subdirectory of the working tree.

git-fsck-cache.txt talks about an "archive", too. However, it then
says "valid tree", when sureley a repository is meant.

Everywhere else, it is called "repository".

 - The act of finding out the object names recorded in "refs" a
   different repository records, optionally updating a local
   "refs" with their values, and retrieving the objects
   reachable from them is called "fetching".  Fetching immediately
   followed by merging is called "pulling".

In that sense, git-http-pull would be more appropriately named
git-http-fetch, and analogous git-ssh-pull.

Also, git-pull-script.txt says "Pull and merge", contradicting this

 - The act of updating "refs" in a different repository with new
   value and populating the object database(s) associated with
   the repository is called "pushing".

 - Currently refs/heads records branch heads of both locally
   created branches and branches fetched from other

 - Currently, fetching always happen against a single branch
   head on a remote repository, and (a remote repository, name
   of the branch) is stored in $GIT_DIR/branches/ as a
   short-hand mechanism.  A file in this directory identifies
   a remote repository by its URL, and the branch to fetch/pull
   from is identified with the URL fragment notation, absense of
   which makes it default to "master".

 - a "pack" usually consists of two files: a file containing objects
   in a compressed format, and an index to the first file. If the
   pack is uncompressed at once (e.g. when git-clone is called), the
   index is not necessary.

git-pack-objects calls this a "packed archive" first, but then reverts
to "pack". git-show-index.txt and git-verify-pack.txt call the .pack file
"packed GIT archive", and the index "idx file". git-unpack-objects.txt
calls the .pack file "pack archive".

I'd also add a short explanation of the following unambiguous terms:

"plumbing", also referred to as "core": the basic set of programs and
scripts usable to half-gods like Linus.

"porcelain", also referred to as "SCM": a thin layer over the plumbing
making GIT usage nice to regular people.

"type": one of the identifiers "commit","tree","tag" and "blob" describing
the type of an object.


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