It's power that gives an aircraft height (5)
I believe the answer is:
might
'it's power' is the definition.
(synonyms)
'an aircraft height' is the wordplay.
'an aircraft' becomes 'mig' (I have seen 'Russian aircraft ' mean 'mig' so perhaps 'aircraft' could also mean 'mig').
'height' becomes 'ht' (abbreviation).
'mig'+'ht'='MIGHT'
'that gives' acts as a link.
(Other definitions for might that I've seen before include "Strength - could possibly" , "intensity of feeling" , "Clout" , "Powerfulness" , "What functions as an auxiliary" .)