Old head of state will cuddle tense man? Heavens! (5)
I believe the answer is:
ether
'heavens' is the definition.
(I've seen this in another clue)
'old head of state will cuddle tense man?' is the wordplay.
I cannot really see how this works, but
'tense' could be 't' (grammatical abbreviation) and 't' is found within the answer.
'man?' could be 'he' (he refers to a man) and 'he' is found within the answer.
'head of state' could be 'er' (abbreviation for Elizabeth Regina) and 'er' is found within the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for ether that I've seen before include "Gas - air - space" , "Anaesthetic is, strangely, there" , "I'm volatile" , "Old anaesthetic -- three (anag)" , "Imaginary interstellar medium" .)