The One Big Happy in my comics feed today (from April 5th originally), with Ruthie putting together the tartar of dental hygiene (as held in check by toothpaste) and the tartar of tartar sauce, going on the resemblance between toothpaste and the sauce commonly accompanying fish:
Here, Ruthie adopts the widespread attitude that Sound/Spelling Rules: an element with the phonology /tártǝr/ or the spelling TARTAR is “the same word” as any other such element (or, at least, is very closely related to it). The opposed attitude — Sense Rules — is also well-known, as evidenced (for example) in some speakers’ hot denials that gay ‘foolish, stupid, unimpressive’ (NOAD2) has anything to do with gay ‘homosexual’.
In the case of tartar, there are two clearly different etymological sources, one having to do with the production of wine (the ultimate source, believe it or not, of the tartar of dental hygiene), the other with inhabitants of Central Asia (the ultimate source, believe it or not, of the tartar of tartar sauce). This is a case where, spectacularly, etymology is not destiny, the two sources of tartar having each split semantically a number of times, each developing into a collection of elements that have nothing much to do with one another beyond sound/spelling, indeed not much more than the descendants of wine tartar have to do with the descendants of Asian tartar; from the point of view of modern speakers, what we’ve got is either a big assortment of distinct lexical items (if you follow Sense Rules resolutely) or a single lexical item with a big heterogeneous assortment of uses (if you follow Sound/Spelling Rules resolutely) — or something in between.