Speedos

From Speedos ("trademark of the Speedo company"), which has become a generic name.

Plural of speedo
(North America, Australia, New Zealand, usually plural) A menâ€²s tight fitting brief swimsuit.

1979, Kent Pearson, Surfing Subcultures of Australia and New Zealand, University of Queensland Press, page 118,For example, board riders paid more attention to appearances (short hair v long hair, speedos v board shorts) and conspicuous behavior (surfing for training rather than for fun or to express oneself), than life savers.
2000 July, Ian Jack (editor), Granta, Issue 70: Australia: The New New World, ISBN 1-929001-00-2, page 42,I remember my mother standing exasperated in the rain with the brolly over her head at dusk while I frog-kicked around in my speedos.
2006, Margaret Henderson, Marking Feminist Times: Remembering the Longest Revolution in Australia, page 212,Their club is Manly, and this word is emblazoned across the back of their speedos.