Definition of oestrual in English:
oestrual
(also estrual)
adjective ˈiːstrʊəlˈiːstrʊlˈɛstrʊəl
Physiology Zoology Origin
Mid 19th century; earliest use found in Robert Mayne (1808–1868). Irregularly from either oestrum or oestrus + -al, after menstrual.