Wife enthralled by ditching bra -- bust's twitching (12)
I believe the answer is:
birdwatching
'twitching' is the definition.
Although both the answer and definition are present participle verbs, I don't see how one could define the other.
'wife enthralled by ditching bra bust's' is the wordplay.
'wife' becomes 'w' (abbreviation).
'enthralled by' means one lot of letters goes inside another ('enthral' can mean 'capture').
'bust's' is an anagram indicator (I've seen 'busted' mean this).
'ditching'+'bra'='ditchingbra'
'ditchingbra' with letters rearranged gives 'birdatching'.
'w' put into 'birdatching' is 'BIRDWATCHING'.
Can you help me to learn more?
(Other definitions for birdwatching that I've seen before include "Ornithology" , "Ornithological hobby" , "Ornithological pursuit" .)