Like horse, tailless bovid’s in biannual event (7)
I believe the answer is:
equinox
'biannual event' is the definition.
(I've seen this before)
'like horse tailless bovid's in' is the wordplay.
I cannot really understand how this works, but
'in' is within the answer.
'bovid' could be 'ox' (ox is a kind of bovid) and 'ox' is located in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for equinox that I've seen before include "Spring or autumn festival" , "Time of day/night equality" , "When the sun crosses the equator" , "March 21st or September 23rd" , "it occurs twice a year" .)