Hat for one pound found during test (6)
I believe the answer is:
trilby
'hat' is the definition.
(I know that trilby is a type of hat)
'one pound found during test' is the wordplay.
'one' becomes 'i' (Roman numeral).
'pound' becomes 'lb' (abbreviation for the unit of weight).
'found during' is an insertion indicator.
'test' becomes 'try' (synonyms).
'i'+'lb'='ilb'
'ilb' placed within 'try' is 'TRILBY'.
'for' acts as a link.
(Other definitions for trilby that I've seen before include "Indented felt hat" , "Type of hat" , "Felt hat with a creased crown" , "du Maurier's heroine" , "Soft hat with indented crown" .)