Stress fixed gape’s not right (5)
I believe the answer is:
ictus
'stress' is the definition.
(I've seen this before)
'gape's not right' is the wordplay.
'gape's' becomes 'rictus'' (rictus is a kind of gape).
'not' is a deletion indicator.
'right' becomes 'r' (common abbreviation).
'rictus' with 'r' removed is 'ICTUS'.
'fixed' acts as a link.
I am not very happy about this link. It may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for ictus that I've seen before include "Metrical stress" , "strokes" , "Seizure" , "Sudden attack" , "recurrence of disease results" .)