Merriam-Webster Collegiate Dictionary - fain

 I. adjective  Etymology: Middle English fagen, fayn, from Old English f?gen; akin to Old English gefeon 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 ~, for the young widow was “altogether fair and lovely…” — Amy Kelly  b. being obliged or constrained ; compelled Great Britain was ~ 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 ~ would blaze — Michael Billington  2.  a. by preference knew it, too, though he would ~ not admit it publicly — John Lukacs  b. by desire I would ~ consult you — W. S. Gilbert