It means very little in Portadown (3)
I believe the answer is:
tad
'it means very little' is the definition.
The definition suggests a singular noun which matches the answer.
'in portadown' is the wordplay.
'in' indicates the answer is hidden within the clue.
'TAD' is hidden in the letters of 'portadown'.
Can you help me to learn more?
(Other definitions for tad that I've seen before include "little boy" , "Slight amount" , "Small amount or degree" , "Small bit" , "(A) bit, touch" .)