Felicity returned one pound to Swiss banks (5)
I believe the answer is:
bliss
'felicity' is the definition.
(bliss is a kind of felicity)
'returned one pound to swiss banks' is the wordplay.
'returned' is a reversal indicator.
'one' becomes 'i' (Roman numeral).
'pound' becomes 'lb' (abbreviation for the unit of weight).
'to' is a charade indicator (letters next to each other).
'banks' suggests removing the centre (the sides or banks of the word).
'swiss' with its middle removed is 'ss'.
'i'+'lb'='ilb'
'ilb' in reverse letter order is 'bli'.
'bli'+'ss'='BLISS'
(Other definitions for bliss that I've seen before include "Sheer delight" , "One who wrote music" , "Rapture; Sir Arthur ---, composer" , "seventh heaven" , "Nirvana" .)