Attempt to hide a one-pound hat (6)
I believe the answer is:
trilby
'hat' is the definition.
(I know that trilby is a type of hat)
'attempt to hide a one-pound' is the wordplay.
'attempt to' becomes 'try' (I've seen this in other clues).
'hide' is an insertion indicator.
'a one' becomes 'I' (Roman numeral).
'pound' becomes 'lb' (abbreviation for the unit of weight).
'i'+'lb'='ilb'
'try' going around 'ilb' is 'TRILBY'.
(Other definitions for trilby that I've seen before include "A man's hat or novel by du Maurier" , "kind of headgear" , "Man's hat or girl hypnotised by Svengali" , "Man's soft felt hat" , "one by du Maurier?" .)