Finally, a Titan joins the titular head (2,4)
I believe the answer is:
at last
'finally' is the definition.
('at last' can be a synonym of 'finally')
'a titan joins the titular head' is the wordplay.
'a titan' becomes 'atlas' (Atlas is an example).
'joins' is a charade indicator (letters next to each other).
'head' indicates taking the first letters.
The first letter of 'titular' is 't'.
'atlas'+'t'='AT LAST'
(Other definitions for at last that I've seen before include "Eventually" , "Finally, after much delay" , "None too soon" , "Finally, after a long wait" , "Finally, having waited a long time" .)