Warm air current (7)
I believe the answer is:
thermal
'warm air current' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for thermal that I've seen before include "Column of rising air used by gliders" , "help for glider" , "Caloric" , "Upward current of warm air" , "Her malt became heat-related" .)