Definition - Adding a letter or syllable to the beginning of a word.

Example -
A-camping we will go!

Etymology -
The word entered English via Latin from Greek, in which it literally means "addition."

Oxford English Dictionary -
Its first citation is from 1553:
"Prosthesis. Of Addition. As thus: He did all to berattle hym. Wherin appeareth that a sillable is added to this woorde (rattle)."
Note: Its synonym prothesis entered English three centuries later.
(T. Wilson Rhet. (1580) 180)

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