sīs .
I Subj. of sum.—
II Contr. from si vis; v. volo init. —
III I. q. suis, v. suus init.
sīs (1) subj.of sum. ...
An Elementary Latin Dictionary
·noun Six. ·see <<Sise>>. II. Sis ·noun A colloquial abbreviation of Sister. ...
Webster's Dictionary of the English Language