Taken as read initially, something black (3)
I believe the answer is:
tar
'something black' is the definition.
(tar is a black substance)
'taken as read initially' is the wordplay.
'initially' says to take the initial letters.
The initial letters of 'taken as read' is 'TAR'.
(Other definitions for tar that I've seen before include "Cigarette substance" , "Harmful tobacco residue" , "Product of burning tobacco" , "Pitch; sailor" , "Mariner, old salt" .)