West opened with lead of trumps for partner (4)
I believe the answer is:
mate
'for partner' is the definition.
(synonyms)
'west opened with lead of trumps' is the wordplay.
'west opened' becomes 'mae' (I can't justify this - if you can you should believe this answer much more).
'with' indicates putting letters inside.
'lead of' suggests taking the first letters (I've seen 'leading' mean this).
The first letter of 'trumps' is 't'.
'mae' placed around 't' is 'MATE'.
Can you help me to learn more?
(Other definitions for mate that I've seen before include "When one can no longer play" , "Fellow member, partner" , "Spouse or informal friend" , "Chess ending; pal" , "Move terminal for King" .)