Put underwear on at home then move to and fro - good idea! (9)
I believe the answer is:
brainwave
'good idea' is the definition.
(I've seen this before)
'put underwear on at home then move to and fro' is the wordplay.
'put underwear on' becomes 'bra' (I can't explain this - if you can you should believe this answer much more).
'at home' becomes 'in' ('I'm in' can mean 'I'm at home').
'then' means one lot of letters go next to another.
'move to and fro' becomes 'wave' (I've seen this before).
'bra'+'in'+'wave'='BRAINWAVE'
Can you help me to learn more?
(Other definitions for brainwave that I've seen before include "Good idea" , "Sudden bright idea" , "Great idea" .)