The American Heritage® Dictionary of the English Language: Fourth Edition. 2000.
Appendix I
Indo-European Roots
ENTRY:
ansu-
DEFINITION:
Spirit, demon. Oldest form *2e/onsu-, colored to *2a/onsu-.1.Aesir; Asgard, from Old Norse ss, god, from Germanic *ansu-.2. Suffixed zero-grade form *su-ro-.Ahura Mazda, Ormazd, from Avestan ahura-, spirit, lord. (Pokorny ansu- 48.)