What does the cryptic crossword clue "Garment that only half suits one (4,2,8)" mean?

The definition is "Garment that only half suits one". The wordplay uses a cryptic definition. Cryptic definition The answer is PAIROFTROUSERS.

Garment that only half suits one (4,2,8)

Guardian Cryptic #28824 | 11 Across | 2022-08-01 flower