Irish anglicized form of Gaelic Ó Deaghaidh, ‘descendant of Deaghadh’, a personal name of uncertain origin. It may be composed of the elements deagh- ‘good’ + ádh ‘luck’, ‘fate’; some such association seems to lie behind its Anglicization as Goodwin.

English and Scottish from a pet form of David.
English nickname from the jackdaw, Middle English dawe, a bird noted for its sleek black color, raucous voice, and thievish nature, any of which characteristics could readily have given rise to a nickname.

This surname is derived from an occupation. 'the deye' or 'day,' a maid, a dairy-maid, whence 'dairy'