Skill in a particular field (7)
I believe the answer is:
prowess
'skill in a particular field' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for prowess that I've seen before include "Skill, expertise; bravery" , "Great ability or daring" , "Bravery in battle" , "Accomplishment" , "Acquired skill(s)" .)