A hundred pounds is always advisable (6)
I believe the answer is:
clever
'advisable' is the definition.
Both the answer and definition are adjectives. Maybe they are linked in a way I don't understand?
'a hundred pounds is always' is the wordplay.
'a hundred' becomes 'C' (Roman numerals).
'pounds' becomes 'L' (L can represent the monetary pound).
'is always' becomes 'ever' (I've seen this before).
'c'+'l'+'ever'='CLEVER'
Can you help me to learn more?
(Other definitions for clever that I've seen before include "Highly intelligent" , "Mentally quick and resourceful" , "easy to teach?" , "Cute" , "Bright; smart" .)