Small group of Iberians dismissed by Republicanism (5)
I believe the answer is:
clump
'small group' is the definition.
(I've seen this before)
'of iberians dismissed by republicanism' is the wordplay.
'of' is an anagram indicator (the answer comes from or 'of' the letters).
'dismissed by' suggests deleting specific letters.
'republicanism' with 'iberians' removed is 'pulcm'.
'pulcm' with letters rearranged gives 'CLUMP'.
(Other definitions for clump that I've seen before include "Clod, lump" , "Rough cluster or heavy tramping sound" , "Dull heavy tread" , "Bunch" , "Compacted mass" .)