Dull girl pursued by Mike (3)
I believe the answer is:
dim
'dull' is the definition.
(I know that dull can be written as dim)
'girl pursued by mike' is the wordplay.
'girl' becomes 'di' ().
'pursued by' is a charade indicator (letters next to each other).
'mike' becomes 'M' (phonetic alphabet: alpha, bravo, charlie etc.).
'di'+'m'='DIM'
(Other definitions for dim that I've seen before include "Without much light" , "Not bright, shadowy" , "& 26 Chinese food selection" , "Not clear or not too bright" , "Opaque, not bright" .)