A chief going heavenwards? The man so ascending is for deification (10)
I believe the answer is:
apotheosis
'for deification' is the definition.
(synonyms)
'a chief going heavenwards? the man so ascending' is the wordplay.
I cannot quite see how this works, but
'a' is present in the answer.
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is present in the answer.
'man' could be 'si' and 'si' is found within the answer.
This explanation may well be incorrect...
'is' acts as a link.
Can you help me to learn more?
(Other definitions for apotheosis that I've seen before include "Elevation to divine status" , "Deification" , "ideal" , "Perfect example" , "Highest point of development" .)