Rest on the bottom (3)
I believe the answer is:
sit
'rest' is the definition.
(I know that rest is a more specific form of the action sit)
'on the bottom' is the wordplay.
'on' means one lot of letters go next to another.
'the' becomes 't' (the is pronounced as a 't' sound in some dialects).
'bottom' becomes 'si' (I can't explain this - if you can you should believe this answer much more).
't' after 'si' is 'SIT'.
Can you help me to learn more?
(Other definitions for sit that I've seen before include "I sell badly the cotton yarn" , "Pose for painter" , "(Of bird) stay on nest" , "Take (an examination)" , "Take a seat; pose" .)