Spoke repeatedly of raid organised on island (5)
I believe the answer is:
radii
'spoke repeatedly of' is the definition.
I can't tell whether this definition defines the answer.
'raid organised on island' is the wordplay.
'organised' is an anagram indicator.
'on' means one lot of letters goes inside another (as in clothing 'on' a person).
'island' becomes 'i' (geographical abbreviation).
'raid' is an anagram of 'radi'.
'radi' placed around 'i' is 'RADII'.
Can you help me to learn more?
(Other definitions for radii that I've seen before include "Lines drawn from a circle's centre" , "spoke with others" , "spoke several times" , "They meet in the middle of a circle" , "more than one spoke" .)