Natural for pub to serve tea (6)
I believe the answer is:
innate
'natural' is the definition.
(I know that natural can be written as innate)
'pub to serve tea' is the wordplay.
'pub' becomes 'inn' (an inn is a type of pub).
'to serve' indicates anagramming the letters (I've seen 'serving' mean this).
'tea' is an anagram of 'ate'.
'inn'+'ate'='INNATE'
'for' acts as a link.
(Other definitions for innate that I've seen before include "Inherent or inborn" , "Born" , "Have tea in inn - it's natural" , "Inborn, natural to (6)" , "not needing to be taught" .)