Aged canine excitedly tense (7)
I believe the answer is:
ancient
'aged' is the definition.
(I've seen this before)
'canine excitedly tense' is the wordplay.
'excitedly' indicates an anagram.
'tense' becomes 't' (abbreviation used in many dictionaries).
'canine' is an anagram of 'ancien'.
'ancien'+'t'='ANCIENT'
(Other definitions for ancient that I've seen before include "from Aristophanes' time" , "very old boy?" , "Extremely old" , "Very old or belonging to times past" , "Antique, old" .)