from Wiktionary, Creative Commons Attribution/Share-Alike License.
superlativeform of plentiful: most plentiful.
Sorry, no etymologies found.
The plentifullest things down here is "dinges", mules and mud, and you very seldom see one without the other.
The Golden Vale in Herefordshire, (being ye pride of al that country,) being the richest yet (for want of employment) the plentifullest place of poore in the kingdom -- yielding two or three hundred folde; the number so increasing (idleness having gotten the upper hand;) if trades bee not raised -- beggery will carry such reputation in my quarter of the country, as if it had the whole to halves.
This place of studie is far betweene the place of the said courts and the cittie of London, which of all thinges necessarie is the plentifullest of all cities and townes of the realme.
(M147) Also, as we haue said before, the said riuer is the plentifullest of fish that euen hath of any man bene seene or heard of, because that from the mouth to the end of it, according to their seasons, you shall finde all sorts of fresh water fish and salt.
Also, as wee have said before, the said ryver is the plentifullest of fyshe that ever hath bene seene or hearde of, because that from the heade to the mouthe of yt you shall finde all kinde of freshe and salt water fyshe accordinge to their season.