Definition of washer noun from the Oxford Advanced Learner's Dictionary

washer

noun
ˈwɒʃə(r)
 
; ˈwɑːʃər
 
; ˈwɔːʃər
 
 
1 a small flat ring made of rubber, metal or plastic placed between two surfaces, for example under a nut (2) to make a connection tight 2 (informal) a washing machine see also dishwasher