From Longman Dictionary of Contemporary Englishtwinsettwin‧set /ˈtwɪnset/ noun [countable] British English DCCa woman’s sweater and cardigan that are meant to be worn together
Examples from the Corpus
twinset• She wore a smart Gor-Ray skirt, always with either a twinset or a wool blouse.• You show me a tweed-skirted twinset and pearl wearer, and I guarantee there's a scarlet bustier pulsating beneath. 