I believe the word ab is a fairly recent addition to the mainstream lexicon.
I guess it stems from our fetishization of the muscular midriff. It’s most often seen in plural form, as in “six-pack abs.” (That’s surely an ironic phrase since drinking six-packs would seem to be at odds with getting a six pack.) I was a little perplexed by the notion of ab in the singular, however. I can’t imagine referring to a single abdominal muscle using this catchall term; one would specify the particular muscle, the rectus abdominis, or whatever. Then I realized ab is most commonly used as not as a noun but an adjective, as in “ab workout.”
Of course you can form quite a few words by adding a single letter to the beginning or end of ab. Common words like cab, dab, gab, jab, lab, nab and tab need no introduction, and the same goes for the aforementioned abs. More obscure is kab, an alternate spelling for cab — not a taxi, but an ancient Hebrew unit of volumetric measure. A sab is someone who sabotages fox hunts for ethical principles. Coming at it from the other end, aba is either a fabric made from goat or camel hair, or a particular kind of garment made from said fabric, a loose-fitting sleeveless number worn by Bedouins. In Australia, at least, abo is a epithet for aboriginal peoples. (But I learned the word when I read Gene Wolfe’s otherworldly Fifth Head of Cerberus.) And how many people remember aby, which is an archaic verb meaning to pay for something? As Demetrius said in A Midsummer Night’s Dream:
Disparage not the faith thou dost not know,
Lest, to thy peril, thou aby it dear.
Finally there’s wab. This one had me stumped for a minute but it appears to be another ethnic slur, according to the excellent Double-Tongued Dictionary.