Schoolgirl’s Dress or Pinafore, a La St Trinians
Puzzle 16 of National Crossword Day Hard Pack
Question is: Schoolgirl’s Dress or Pinafore, a La St Trinians
and the answer is: GYMSLIP
Word Meaning:
GYMSLIP — A sleeveless tunic with a pleated skirt, most commonly seen as part of a girl's school uniform.
Definitions from Wiktionary.