Attempt to secure one pound for a hat (6)
I believe the answer is:
trilby
'a hat' is the definition.
(trilby is a kind of hat)
'attempt to secure one pound' is the wordplay.
'attempt' becomes 'try' (I've seen this before).
'to secure' means one lot of letters goes inside another.
'one' becomes 'i' (Roman numeral).
'pound' becomes 'lb' ('lb' can be a synonym of 'pound').
'i'+'lb'='ilb'
'try' going around 'ilb' is 'TRILBY'.
'for' acts as a link.
(Other definitions for trilby that I've seen before include "one by du Maurier?" , "Hat named after fictional character" , "kind of headgear" , "Miss O'Ferrall" , "Man's hat or girl hypnotised by Svengali" .)