Infantryman pays for a venerable fellow to the bitter end (4,7)
I believe the answer is:
foot soldier
'infantryman' is the definition.
(synonyms)
'pays for a venerable fellow to the bitter end' is the wordplay.
I cannot really see how this works, but
'pays' could be 'foots' (footing is a kind of paying) and 'foots' is found within the answer.
'venerable' could be 'old' (similar in meaning) and 'old' is present in the answer.
The remaining letters 'ier' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for foot soldier that I've seen before include "Infantryman" , "Valuable but lowly worker" .)