c. 1300, preiere, "earnest request, entreaty, petition," also "the practice of praying or of communing with God," 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" (from PIE root *prek- "to ask, entreat").
From mid-14c. as "devout petition to God or a god or other object of worship;" also "the Lord's Prayer;" also "action or practice of praying." Related: Prayers. Prayer-book "book of forms for public or private devotions" is attested from 1590s; prayer-meeting "service devoted to prayer, sacred song, and other religious exercises" is from 1780. Prayer-rug "small carpet spread and used by a Muslim when engaged in devotions" is by 1898 (prayer-carpet is by 1861). To not have a prayer "have no chance" is from 1941.