Etymology: Middle English plente, from Anglo-French plenté, from Late Latin plenitat-, plenitas, from Latin, fullness, from plenus full — more at full
Date: 13th century
a. a full or more than adequate amount or supply <had plenty of time to finish the job> b. a large number or amount <in plenty of trouble> 2. the quality or state of being copious ; plentifulness II. adjective Date: 14th century 1. plentiful in amount, number, or supply <if reasons were as plenty as blackberries — Shakespeare> 2. ample <plenty work to be done — Time> Usage: Many commentators object to use of sense 2 in writing; it appears to be limited chiefly to spoken English. Sense 1 is literary but is no longer in common use. III. adverb Date: 1842 more than sufficiently ; to a considerable degree <the nights were plenty cold — F. B. Gipson> Usage: Many handbooks advise avoiding the adverb plenty in writing; “use very, quite, or a more precise word,” they advise. Actually plenty is often a more precise word than its recommended replacements; very, fully, or quite will not work as well in these typical quotations <it's already plenty hot for us in the kitchen without some dolt opening the oven — C. H. Bridges> <may not be rising quite as rapidly as other health costs, but it is going up plenty fast — Changing Times>. It is not used in more formal writing.
New Collegiate Dictionary. 2001.