Crossword Genius

Rough edge in cavity I have (9)

Ross

I believe the answer is:

primitive

'rough' is the definition.
(thesaurus)

'edge in cavity i have' is the wordplay.
'edge' becomes 'rim' (rim is a kind of edge).
'in' means one lot of letters goes inside another.
'cavity' becomes 'pit' ('pit' can be a synonym of 'cavity').
'i have' becomes 'ive'.
'rim' going within 'pit' is 'primit'.
'primit'+'ive'='PRIMITIVE'

(Other definitions for primitive that I've seen before include "At a very early stage of development" , "Old painter" , "Ancient" , "Original - uncivilised" , "Not sophisticated" .)

I've seen this clue in The Independent.
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