Green’s Dictionary of Slang

1. (Aus.) a swim.

1965

Aus. Women’s Wkly 3 Nov. 10/4: If you went for a dim sim (swim) you had to watch out for the Noah’s arks (sharks).

2. (Aus. prison) a criminal [= crim n.].

1990

Tupper & Wortley Aus. Prison Sl. Gloss. 🌐 Dim Sim. Criminal.