DSL - SND1 DU, Doo, pron. and v. Also dou (Sh. 1866 Edm. Gl.).
1. pron. Sh. and Ork. forms of thou, used by parents to children, old persons to young, or between familiar friends or equals (Sh. 1950). In Orkney, the more common form is thoo, but this return to the th sound is fairly recent (Ork. 1929 Marw.).
*Sh. 1836 in Gentleman's Mag. II. 590:
Du an I hez a kra ta pluk afoar wee pairt.
*Sh. 1898 ``Junda'' Klingrahool 24:
So, weel I wat du's tired da nicht, Efter da day't du's hed.
*Sh. 1922 J. Inkster Mansie's Röd 5:
Is doo in, Sibbie?
2. v. To address a person as ``thou'', to address familiarly (Sh. 1866 Edm. Gl.; 1908 Jak. (1928)).
*Sh. 1914 Angus Gl.:
He wid no du da dog.
[Norw. du, O.N. þú, thou; Icel. þúa, Norw. dua, to address as ``du''. For change of O.N. ð to Sh., Ork. d, see Jak. Intro. V. § 29; Marw. p. xliv. Cf. also O.Sc. dow, to address as ``thou'', c.1470.]