Is on terra firma for Easter say (6)
I believe the answer is:
island
'for easter say' is the definition.
(Easter Island is an example)
'is on terra firma' is the wordplay.
'on' means one lot of letters go next to another (in a down clue, letters appear on others).
'terra firma' becomes 'land' (synonyms).
'is'+'land'='ISLAND'
(Other definitions for island that I've seen before include "See 14" , "Eg, eyot or inch" , "Man perhaps" , "See 2" , "Malta, say" .)