Origin of sis
Examples from the Web for sises
Cf. 'At Sessions and at Sises we bare the stroke and swaye.'Chaucer's Works, Volume 5 (of 7) -- Notes to the Canterbury Tales|Geoffrey Chaucer
Word Origin for sis
1650s, abbreviated form of sister; in American English, applied generally to girls and young women (1859). It also was the familiar short form of Cecilie, Cicely, a common name for girls in the Middle English period.