Be of one mind about English silver, first (5)
I believe the answer is:
agree
'be of one mind' is the definition.
(two people who are of one mind are in agreement)
'about english silver first' is the wordplay.
'about' becomes 're' (regarding).
'english' becomes 'E' (abbreviation as in OED).
'silver' becomes 'Ag' (Ag is the chemical symbol for silver).
'first' is a charade indicator (letters next to each other).
're'+'e'='ree'
'ree' put after 'ag' is 'AGREE'.
(Other definitions for agree that I've seen before include "Accord, match" , "Go along with" , "Accept" , "Be of one mind" , "suit" .)