prayer (n.) Look up prayer at Dictionary.com
c.1300, from Old French prier "prayer, petition, request" (12c., Modern French prière), from Medieval Latin precaria "petition, prayer," noun use of Latin adjective precaria, fem. of precarius "obtained by prayer, given as a favor," from precari "to ask, beg, pray" (see pray). Related: Prayers.

Prayer-book attested from 1590s; prayer-meeting from 1780. To not have a prayer "have no chance" is from 1941.