Father, I conclude, extremely likely to be amiable (8)
I believe the answer is:
friendly
'be amiable' is the definition.
(similar in meaning)
'father i conclude extremely likely' is the wordplay.
'father' becomes 'fr' (abbreviation as in a priest's title).
'conclude' becomes 'end' (I've seen this in another clue).
'extremely' says to hollow out the word (remove centre letters) (only the extremes of the word are used).
'likely' with its centre taken out is 'ly'.
'fr'+'i'+'end'+'ly'='FRIENDLY'
'to' acts as a link.
(Other definitions for friendly that I've seen before include "Amicable and kindly" , "match?" , "Sociable" , "prepared to talk to fellow passengers?" , "One is obviously on good terms with" .)