Aeronauts needs this sp___ (3,3)
I believe the answer is:
hot air
'aeronauts needs this sp' is the definition.
The definition suggests a singular noun which matches the answer.
This is all the clue.
Can you help me to learn more?
(Other definitions for hot air that I've seen before include "Boastful talk or balloon filler" , "Empty bombast often found in balloon" , "Boastful talk or balloon filling" , "Bluster" , "Empty or boastful talk - good for balloons" .)