He has to look out for the best conclusion (5)
I believe the answer is:
peter
'he' is the definition.
(I've seen this before)
'to look out for the best conclusion' is the wordplay.
'to look' becomes 'pe' (I am not sure about this - if you are sure you should believe this answer much more).
'out' indicates anagramming the letters.
'conclusion' says to take the final letters.
The last letters of 'for the best' are 'ret'.
'ret' is an anagram of 'ter'.
'pe'+'ter'='PETER'
'has' is the link.
Can you help me to learn more?
(Other definitions for peter that I've seen before include "Sir - - Ustinov" , "Blue -, ship's flag" , "Rock-like apostle" , "Play high card before low" , "Dwindle away to nothing" .)