Join together to thoroughly search home, last in terrace (7)
I believe the answer is:
combine
'join together' is the definition.
'thoroughly search home last in terrace' is the wordplay.
'thoroughly search' becomes 'comb'.
'home' becomes 'in' ('he's home' can mean 'he's in').
'last in' indicates one should take the final letters.
The last letter of 'terrace' is 'e'.
'comb'+'in'+'e'='COMBINE'
'to' acts as a link.
(Other definitions for combine that I've seen before include "Association" , "alloy" , "Unite; -- harvester" , "Unite, merge" , "Unite; some farm machinery" .)