That is upsetting laymen (6)

I believe the answer is:

namely

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

'upsetting laymen' is the wordplay.
'upsetting' indicates anagramming the letters.
'laymen' with letters rearranged gives 'NAMELY'.

(Other definitions for namely that I've seen before include "Videlicet" , "That is to say, specifically" , "to wit" , "Viz" , "Old especially" .)

I've seen this clue in The Telegraph.

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