aetiology | etiology,

n.
[‘ The assignment of a cause; the provision of a reason for something; (also) the cause assigned, the reason given for something.’]

Etymology: < classical Latin aetiologia inquiry into, or explanation of, causes,
in post-classical Latin also in medical context (1602 or earlier) < ancient Greek αἰτιολογία < αἰτία responsibility, guilt, blame, accusation, cause, reason
( < αἴτιος culpable, responsible
< an unattested noun (compare ἔξαιτος choice, excellent)
< the stem of αἴνυσθαι to take hold of, seize
( < the same Indo-European base as Tocharian B ai- to give) + -τος, suffix forming adjectives)
+ -λογία -LOGY comb. form.

Compare Middle French aitiologie, French étiologie, †aetiologie (1550 in an apparently isolated attestation, and subsequently from 1694, in medical context; 1611 in philosophical context),
Spanish etiología (1580),
Italian eziologia (1631 as †etiologia; earliest in medical context).