Attempt to secure one pound for felt hat (6)
I believe the answer is:
trilby
'felt hat' is the definition.
(synonyms)
'attempt to secure one pound' is the wordplay.
'attempt to' becomes 'try' (I've seen this in other clues).
'secure' is an insertion indicator (inserted letters are secured inside).
'one' becomes 'i' (Roman numeral).
'pound' becomes 'lb' (abbreviation for the unit of weight).
'i'+'lb'='ilb'
'try' placed around 'ilb' is 'TRILBY'.
'for' is the link.
(Other definitions for trilby that I've seen before include "Sinatra's hat?" , "Impressionable singer" , "Man's soft felt hat" , "Soft hat with indented crown" , "It was felt to provide capital cover" .)