That is a sign of penitence, in a way (8)

I believe the answer is:

scilicet

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'that is' is the definition.
(I've seen this before)

'a sign of penitence in a way' is the wordplay.
'a sign of penitence' becomes 'cilice' (I can't explain this - if you can you should believe this answer much more).
'in' is an insertion indicator.
'a way' becomes 'st' (abbreviation for street).
'cilice' going into 'st' is 'SCILICET'.

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(Other definitions for scilicet that I've seen before include "That is to say" , "Introduction to explanation" , "Namely" .)

I've seen this clue in The Sunday Times and The Times.

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