Abandon rear of house completely (5)
I believe the answer is:
quite
'completely' is the definition.
(thesaurus)
'abandon rear of house' is the wordplay.
'abandon' becomes 'quit' (quitting is a kind of abandoning).
'rear of' says to take the final letters.
The final letter of 'house' is 'e'.
'quit'+'e'='QUITE'
(Other definitions for quite that I've seen before include "Completely or entirely - be quiet" , "Fairly; indeed" , "Somewhat - I agree" , "To a degree" , "Somewhat; fully" .)