early 13c., "ask earnestly, beg,"
also (c. 1300) "pray to a god or saint,"
from Old French preier "to pray" (c.900, Modern French prier),
from Vulgar Latin *precare (also source of Italian pregare),
from Latin precari "ask earnestly, beg, entreat,"
from *prex (plural preces, genitive precis) "prayer, request, entreaty,"
from PIE root *prek- "to ask, request, entreat"
(cognates: Sanskrit prasna-, Avestan frashna- "question;"
Old Church Slavonic prositi, Lithuanian prasyti "to ask, beg;"
Old High German frahen, German fragen, Old English fricgan "to ask" a question).

Parenthetical expression I pray you, "please, if you will," attested from 1510s, contracted to pray 16c. Related: Prayed; praying. Praying mantis attested from 1809. The "Gardener's Monthly" of July 1861 lists other names for it as camel cricket, soothsayer, and rear horse.