Upset postmistress? Not half! (6)

I believe the answer is:

stress

'upset' is the definition.
(thesaurus)

'postmistress? not half' is the wordplay.
'not half' means to take half the letters.
'postmistress' cut in half is 'STRESS'.

(Other definitions for stress that I've seen before include "Dwell on" , "Underline - tension" , "Tension, pressure" , "nervous tension" , "Force" .)

I've seen this clue in The Telegraph.

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