Joint vote wrongly cast in Irish parliament (8)
I believe the answer is:
'joint' is the definition.
(dovetail joint is a kind of joint)
'vote wrongly cast in irish parliament' is the wordplay.
'wrongly' indicates an anagram.
'cast in' means one lot of letters goes inside another.
'irish parliament' becomes 'dail' (I've seen this before).
'vote' is an anagram of 'ovet'.
'ovet' inserted within 'dail' is 'DOVETAIL'.
(Other definitions for dovetail that I've seen before include "Joint - fit neatly" , "Fit snugly" , "Interlocking joint" , "Joint with fan-shaped tenon" , "Kind of joint" .)