Green’s Dictionary of Slang

1. (Anglo-Irish) an umbrella.

1937–84

Partridge DSUE (1984) 1213: —1904.

2. (US Und.) a prison cell.

1914

Jackson & Hellyer Vocab. Criminal Sl.

3. (US prison) prison uniform; civilian clothes.

1929		C.G. Givens ‘Chatter of Guns’ in Sat. Eve. Post 13 Apr.; list extracted in AS VI:2 (1930) 134: tent, n. Prison uniform. Also a suit of clothes.
1949		Monteleone Criminal Sl. (rev. edn).
1950		Goldin et al. DAUL 221/1: Tent. (P; very common, scattered areas) A prison inmate’s uniform, notoriously ill-fitting.

4. any form of ill-fitting garment.

1956

‘Ed Lacy’ Men from the Boys 🌐 He glanced at the way my suit hung on me, asked, ‘A circus come with that tent?’.