Mostly tense character in Euripides, say? (3)
I believe the answer is:
tau
'character in euripides say?' is the definition.
(Greek letter - Euripedes was a Greek dramatist)
'mostly tense' is the wordplay.
'mostly' means to remove the last letter.
'tense' becomes 'taut' (similar in meaning).
'taut' with its final letter removed is 'TAU'.
(Other definitions for tau that I've seen before include "Foreign character" , "Homeric character" , "Marathon character" , "Greek character" , "character from Athens" .)