Says about first of three remains (5)
I believe the answer is:
stays
'remains' is the definition.
(to stay in a place is to remain there)
'says about first of three' is the wordplay.
'about' means one lot of letters goes inside another.
'first of three' becomes 't' (1st letter of 'three').
'says' enclosing 't' is 'STAYS'.
(Other definitions for stays that I've seen before include "... holidays" , "old underwear" , "for a slimmer figure" , "Remains (in place)" , "Remains; supporting wires" .)