Dress caught on a black taxi (7)
I believe the answer is:
minicab
'taxi' is the definition.
(I know that minicab is a type of taxi)
'dress caught on a black' is the wordplay.
'dress' becomes 'mini' (mini dress).
'caught on' becomes 'c' (cricket abbreviation. I am not sure about the 'on' bit.).
'black' becomes 'b' (abbreviation as in pencil hardness).
'mini'+'c'+'a'+'b'='MINICAB'
(Other definitions for minicab that I've seen before include "Type of taxi" , "It can't be hailed in the street" , "Metered vehicle for hire" , "Hired vehicle" , "Car used as taxi" .)