From Longman Dictionary of Contemporary Englishgymslipgym‧slip /ˈdʒɪmˌslɪp/ noun [countable] British English DCCDSa type of dress without sleeves that girls wore in the past over a shirt as a part of their school uniform
Examples from the Corpus
gymslip• I'd get a gymslip - blue, not green - for Redhill Grammar, some time soon when we went home.• The gymslip Lolita is not entirely a figment of the male imagination. 