The Collaborative International Dictionary of English v.0.48:
backrest \back"rest\ n. 1. a support that you can lean against while sitting. Syn: back. [WordNet 1.5]WordNet (r) 3.0 (2006):
backrest n 1: a support that you can lean against while sitting; "the back of the dental chair was adjustable" [syn: back, backrest]