The American Heritage® Dictionary of the English Language: Fourth Edition. 2000.
Appendix I
Indo-European Roots
ENTRY:
swesor-
DEFINITION:
Sister. Perhaps originally a compound of s(w)e- and *esr, woman, so literally “woman of one's own kin group” in an exogamous society. 1. Zero-grade form *swesr-.a.sister, from Old English sweostor, sister, and Old Norse systir, sister, both from Germanic *swestr-;b. suffixed form *swesr-no-.cousin, from Latin sobrnus, maternal cousin. 2.sororal, sorority; sororicide, from Latin soror, sister. (Pokorny sesor- 1051.)
r, woman, so literally “woman of one's own kin group” in an exogamous society. 1. Zero-grade form *swesr-. a. sister, from Old English sweostor, sister, and Old Norse systir, sister, both from Germanic *swestr-; b. suffixed form *swesr-
no-. cousin, from Latin sobr
esor- 1051.) 
