Old letter S (4)

I believe the answer is:

ogee

's' is the definition.
(S-shaped architectural feature)

'old letter' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'letter' becomes 'gee' (G**).
'o'+'gee'='OGEE'

(Other definitions for ogee that I've seen before include "Leer" , "architectural feature" , "bit of Gothic architecture?" , "S-shaped line" , "S-shaped curve" .)

I've seen this clue in The Times.

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