Anticipate no relaxation during trip (9)
I believe the answer is:
'anticipate' is the definition.
(I know that anticipate can be written as forestall)
'no relaxation during trip' is the wordplay.
'no' becomes 'O' (resembles 0 - 'no' can mean 'zero').
'relaxation' becomes 'rest' (synonyms).
'during' indicates putting letters inside.
'trip' becomes 'fall' (trip can mean to fall over).
'orest' placed inside 'fall' is 'FORESTALL'.
(Other definitions for forestall that I've seen before include "Avert" , "Anticipate" , "Take action before" , "Stop" , "Hinder by anticipation" .)