Old canine weirdly beginning to talk (7)
I believe the answer is:
ancient
'old' is the definition.
(similar in meaning)
'canine weirdly beginning to talk' is the wordplay.
'weirdly' indicates an anagram.
'beginning to' indicates taking the first letters.
The initial letter of 'talk' is 't'.
'canine' anagrammed gives 'ancien'.
'ancien'+'t'='ANCIENT'
(Other definitions for ancient that I've seen before include "very old boy?" , "Veteran" , "Archaic" , "so old-fashioned" , "Nice tan (anag.)" .)