Thinks back about arms and legs (9)
I believe the answer is:
remembers
'thinks back' is the definition.
('remember' can be a synonym of 'think back')
'about arms and legs' is the wordplay.
'about' becomes 're' ('re' means regarding or about).
'arms and legs' becomes 'members' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
're'+'members'='REMEMBERS'
Can you help me to learn more?
(Other definitions for remembers that I've seen before include "Recalls to mind" , "Recalls from memory" , "Commemorates" , "Celebrates" , "Recollects" .)