In Dundalk, a little base (6)
I believe the answer is:
alkali
'base' is the definition.
(synonyms)
'in dundalk a little' is the wordplay.
'in' indicates the answer is hidden within the clue.
'ALKALI' is hidden in the letters of 'dundalk a little'.
(Other definitions for alkali that I've seen before include "base solution" , "Eg, lime or caustic soda" , "Substance turning litmus paper blue" , "bases" , "Acid-neutralising substance" .)