Refers to a person who makes a request or petition, often in a formal or religious context. The 'prayer' sense is literal, as in one who prays at a shrine or temple.
The supplicant prayed for family safety at the shrine.
The number of applicants for this scholarship is increasing every year.
Compound of 願い (negai, 'wish, request') and 主 (nushi, 'master, owner, person'). The exact historical derivation is uncertain, but the word literally means 'the person of the request'.