Crossword Genius

Uncool underwear (8)

Ross

I believe the answer is:

thermals

'underwear' is the definition.
(I know that thermals is a type of underwear)

I cannot understand how the remainder of the clue works.

(Other definitions for thermals that I've seen before include "Warm underwear" , "Lest harm come to rising currents of air" , "for gliders?" , "Warm clothes" , "Rising currents of hot air" .)

I've seen this clue in The Guardian.
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