Definition of sister-in-law noun from the Oxford Advanced Learner's Dictionary

 

sister-in-law

 noun
noun
BrE BrE//ˈsɪstər ɪn lɔː//
 
; NAmE NAmE//ˈsɪstər ɪn lɔː//
 
(pl. sisters-in-law) Marriage, Relations
 
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the sister of your husband or wife; your brother’s or sister's wife; the wife of your husband or wife’s brother compare brother-in-law See related entries: Marriage, Relations
See the Oxford Advanced American Dictionary entry: sister-in-law