Function in trigonometry (abbr) (5)

I believe the answer is:

cosec

(Other definitions for cosec that I've seen before include "Inverse of sine (abbr.)" , "(In maths) reciprocal of sine (abbr)" , "company secretary" , "Trig function" , "(In mathematics) the reciprocal of sine (abbr)" .)

I've seen this clue in The Guardian.

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