To get a hundred pounds is always smart (6)
I believe the answer is:
clever
'smart' is the definition.
(similar in meaning)
'to get a hundred pounds is always' is the wordplay.
'to get' means one lot of letters go next to another.
'a hundred' becomes 'C' (Roman numerals).
'pounds' becomes 'l' (currency sign).
'is always' becomes 'ever' (I've seen this before).
'c'+'l' is 'cl'.
'cl'+'ever'='CLEVER'
(Other definitions for clever that I've seen before include "Quick, skilful" , "Mentally quick and resourceful" , "Bright - ingenious" , "Gifted" , "Smart or quick at learning" .)