Cf. 'At Sessions and at sises we bare the stroke and swaye.'
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.
Risky; succeed-or-be-ruined: Playing cornerback in the National Football League, particularly for a young player, is a sink-or-swim proposition (1668+)