Uncool underwear (8)
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" .)