Time when day and night are of equal length (7)

I believe the answer is:

equinox

(Other definitions for equinox that I've seen before include "It occurs in September and March" , "Vernal - -" , "Spring or autumn festival" , "Time of equal day and night length" , "March 21st or September 23rd" .)

I've seen this clue in the Sydney Morning Herald.

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