I. ˈfān adjective
Etymology: Middle English fagen, fayn, from Old English fægen; akin to Old English gefēon to rejoice, Old High German gifehan, Old Norse feginn happy
Date: before 12th century
1. archaic : happy , pleased
2. archaic : inclined , desirous
3.
a. : willing
he was very fain , for the young widow was “altogether fair and lovely…” — Amy Kelly
b. : being obliged or constrained : compelled
Great Britain was fain to devote its whole energy…to the business of slaying and being slain — G. M. Trevelyan
II. adverb
Date: 12th century
1. : with pleasure : gladly
a speech of fire that fain would blaze — Michael Billington
2.
a. : by preference
knew it, too, though he would fain not admit it publicly — John Lukacs
b. : by desire
I would fain consult you — W. S. Gilbert