Strong alpha males? Beginning to think this is heavenly (9)
I believe the answer is:
firmament
'this is heavenly' is the definition.
(the firmament is the heavens)
'strong alpha males? beginning to think' is the wordplay.
'strong' becomes 'firm' (synonyms).
'alpha' becomes 'a' (phonetic alphabet: alpha, bravo, charlie etc.).
'males?' becomes 'men' (man is a kind of male).
'beginning to' says to take the initial letters.
The first letter of 'think' is 't'.
'firm'+'a'+'men'+'t'='FIRMAMENT'
(Other definitions for firmament that I've seen before include "The starry heaven" , "Sky (literary)" , "Heavens, sky" , "outer space, encapsulated" , "The celestial sphere" .)