Go astray or slip (5)

I believe the answer is:

error

'slip' is the definition.
(thesaurus)

'go astray or' is the wordplay.
'go astray' becomes 'err' (I've seen this before**).
'err'+'or'='ERROR'

(Other definitions for error that I've seen before include "Miscarriage of justice" , "Solecism" , "Fallacy, mistake" , "Way of operating" , "Bug" .)

I've seen this clue in The Globe and Mail and The Telegraph.

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