Measure sharp troops with time for poisoning (12)
I believe the answer is:
embitterment
'poisoning' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'measure sharp troops with time' is the wordplay.
'measure' becomes 'em' (em is a unit of measurement used by printers).
'sharp' becomes 'bitter' (I've seen this before).
'troops' becomes 'men' (both can mean soldiers).
'with' says to put letters next to each other.
'time' becomes 't' (abbreviation).
'em'+'bitter'+'men'+'t'='EMBITTERMENT'
'for' is the link.
Can you help me to learn more?
(Other definitions for embitterment that I've seen before include "The arising of resentful hostility" , "Sourness" , "Grudge" .)