Around the water cooler at Language Log Plaza yesterday, David Beaver noted a HuffPo headline "With Pitfalls Abound For Prosecutors, Could Edwards Case Fall Apart?", where abound is used like aplenty. He also reported that a quick web search turns up many examples where abound is used like afoot: "speculation is abound", "excitement is abound".
Words like aplenty and afoot are etymologically prepositional phrases, with the a- being etymologically a variant of the English preposition on or in. Since prepositional phrases can be post-nominal modifiers ("men on base") and predicatives ("they're on call"), it's reasonable for such words to retain some of these uses.
Abound, on the other hand, comes as a verb (by way of Norman French) from Latin abundare, or in more detail from the OED:
< Anglo-Norman abunder, abounder, habonder, habounder, Anglo-Norman and Old French, Middle French abonder, Anglo-Norman and Middle French habunder (French abonder) (with de or en) to have (something) in a large quantity (first half of the 12th cent.), to exist in a large quantity (late 12th cent.) < classical Latin abundāre to overflow, to emanate, issue, or spring forth, to flow copiously, to be full (of a liquid), to be plentifully supplied, to be rich in, to have plenty, to have an excess, to be plentiful or numerous, to be superfluous < ab- prefix1 + undāre to flow in waves (see undation n.).
At first, I thought that the adjectival uses of abound must come from re-analysis by analogy to words like a-plenty and a-foot. But the OED tells us that an adjectival version of abound has apparently been Out There for a long time. The OED gives it a slightly different etymology:
Originally < Middle French habonde abundant (15th cent.) < classical Latin abundus having plenty of water (2nd cent. a.d.), either < abundē abundantly ( < abundāre abound v.1 + -ē, suffix forming adverbs) or directly < abundāre abound v.1; in later use probably independently < abound v.1 Compare earlier abundant adj.
And the citations start in 1425:
c1425 Lydgate Troyyes Bk. (Augustus A. 4) i. 4014 Troye town‥Of gold and tresour is passyngly habounde.
a1450 Generides (Helm.) (1865) 10049 Of plentie thus he was abound To hem al that he his frendes found.
a1475 (1430) Lydgate tr. G. Deguileville Pilgrimage Life Man (Vitell.) 21046 A merssh lond‥off ffylthes ryht habounde.
a1500 (1422) Lydgate Life Our Lady (Adv.) (1843) 92 The streme of sapience Of whyche the flod most july is habownd.
1851 Constit. Albany Man. Labor Acad. 3 in Jrnl. Afr. Amer. Hist. 87 185 This is essential also, to counteract a spirit of aristocracy, that is abound in the earth.
2000 P. K. Rao World Trade Organization & Environment i. 3 The long history and tradition of inter-regional trade is abound with multiple and varied experiences.
The OED confesses that this form is "now rare" — certainly none of us around the water cooler recalled ever having encountered it before.
Returning to the a-NOUN words, the OED explains that
The separate preposition a ceased to be used in standard English after about 1700, being replaced by the full on, in, or the various prepositions which represent them in modern idiom, surviving only in a few set uses […] such as to go a begging, to set a going […], and in temporal distributive phrases, as twice a day, once a year, where it had been early identified with the indefinite article […]. It also survived in a large number of combinations, where it was treated as a prefix to the governed word […].
Common examples are abed, aboard, afield, ashore, afire, afloat, ajar, alive, asleep, afoot. aside, asunder.
it's interesting that many of these have developed or retained idiosyncratic constructional distributions, e.g. "There's water a-plenty", "??Water is a-plenty".
(I'm sorry to say that the HuffPo headline has apparently been regularized to "John Edwards Case: Pitfalls Abound For Prosecutors".)