Constellation Greek character starts to recognise using specs (6)
I believe the answer is:
taurus
'constellation' is the definition.
(Taurus is an example)
'greek character starts to recognise using specs' is the wordplay.
'greek character' becomes 'tau' (letter from the Greek alphabet**).
'starts to' suggests taking the first letters.
The initial letters of 'recognise using specs' is 'rus'.
'tau'+'rus'='TAURUS'
(Other definitions for taurus that I've seen before include "April/May sign" , "Sign of the Bull from 12 across" , "Zodiacal bull" , "A group of stars" , "Bull star sign" .)