Power giving an aircraft height (5)
I believe the answer is:
might
'power' is the definition.
(synonyms)
'giving an aircraft height' is the wordplay.
'giving' means one lot of letters go next to another.
'an aircraft' becomes 'mig' (I have seen 'Russian aircraft ' mean 'mig' so perhaps 'aircraft' could also mean 'mig').
'height' becomes 'ht' (abbreviation).
'mig' put next to 'ht' is 'MIGHT'.
(Other definitions for might that I've seen before include "Clout" , "is not unlikely to" , "word expressing possibility" , "What functions as an auxiliary" , "- - and main" .)