Hostile incursions into Greek island say (7)
I believe the answer is:
inroads
'hostile incursions' is the definition.
(I've seen this before)
'into greek island say' is the wordplay.
'into' becomes 'in'.
'greek island' becomes 'rhodes' (Rhodes is a Greek island).
'say' indicates a 'sounds like' (homophone) clue.
'rhodes' is a homophone of 'roads'.
'in'+'roads'='INROADS'
(Other definitions for inroads that I've seen before include "advances" , "(Make) raids, intrusions (into)" , "Progress" , "Ordains as offensives" , "Making them is reductive" .)