Remove from under a seat (5)
I believe the answer is:
erase
'remove' is the definition.
(to erase is to remove)
'from under a seat' is the wordplay.
'from' indicates a hidden word.
'ERASE' can be found hidden inside 'under a seat'.
(Other definitions for erase that I've seen before include "Remove recorded material" , "Obliterate" , "Remove, wipe out" , "Remove all traces of" , "Remove from memory" .)