American Dictionary of the English Language

WELKIN, noun [G., a cloud.] The visible regions of the air; the vault of heaven. [This is obsolete, unless in poetry.]

WELKIN eye, in Shakespeare, is interpreted by Johnson, a blue eye, from welkin the sky; by Todd, a rolling eye, from Sax. Wealcan, to roll; and by Entick, a languishing eye. See Welk. It is obsolete, at least in New England.