The slow number I'm after (3)
I believe the answer is:
dim
'the slow' is the definition.
(I've seen this before)
'number i'm after' is the wordplay.
'number' becomes 'd' (D is an example).
'after' means one lot of letters go next to another.
'd'+'im'='DIM'
(Other definitions for dim that I've seen before include "reduce volume" , "Unintelligent; badly lit" , "Vague" , "Lacking clarity or distinctness" , "& 26 Chinese food selection" .)