Crossword Genius

Glider pilots find them uplifting (8)

Ross

I believe the answer is:

thermals

I'm a little stuck... Click here to teach me more about this clue!

'glider pilots' is the definition.
Although both the answer and definition are plural nouns, I cannot understand how they can define each other.

I can't explain the rest of the clue.

Can you help me to learn more?

(Other definitions for thermals that I've seen before include "Upward air currents - winter warmers" , "for gliders?" , "Warm underwear" , "Long johns" , "Warm clothes" .)

I've seen this clue in The Globe and Mail.
Want a hint initially instead of a full solution? Install my app