Crossword Genius

Copper put on special point (4)

Ross

I believe the answer is:

cusp

'point' is the definition.
(I know that cusp is a type of point)

'copper put on special' is the wordplay.
'copper' becomes 'cu' (chemical symbol).
'put on' is a charade indicator (letters next to each other).
'special' becomes 'sp' (abbreviation).
'cu'+'sp'='CUSP'

(Other definitions for cusp that I've seen before include "Pointed end - division between signs of the zodiac" , "Pointed end where two curves meet" , "Point formed by two intersecting curves - point of transition" , "Pointed end (e.g. on tooth)" , "Turning point on which important developments depend" .)

I've seen this clue in The Times.
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