Old old Scotsman’s outside loop (5)
I believe the answer is:
picot
'loop' is the definition.
(small loop or loops in embroidery or lace)
'old old scotsman's outside' is the wordplay.
'old' becomes 'o' (abbreviation as in OT - Old Testament).
'old scotsman' becomes 'pict' (I've seen this in another clue. I am not sure about the 'old' bit.).
'outside' is an insertion indicator (some letters go outside others).
'o' placed into 'pict' is 'PICOT'.
Can you help me to learn more?
(Other definitions for picot that I've seen before include "ornament" , "Loopy series" , "loopy decoration" , "Small embroidery loop" , "Pattern of small loops, as in lace" .)