Firm retains most beneficial item under pressure (8)
I believe the answer is:
strained
'under pressure' is the definition.
(I've seen this before)
'firm retains most beneficial item' is the wordplay.
I cannot really see how this works, but
an anagram of 'retains' is 'straine' which is located in the answer.
A single letter 'd' remains 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 strained that I've seen before include "Not relaxed; laboured" , "Forced -- like baby food?" , "taxed" , "Passed through a sieve" , "Stretched, extended to the limit" .)