 The name Sif is the singular form of the plural Old Norse word sifjar. Sifjar only appears in singular form when referring to the goddess as a proper noun. Sifjar is cognate to the Old English sib (meaning "affinity, connection, by marriage") and in other Germanic languages: Gothic language sibja, Old High German sibba, and German Sippe. Sifjar appears not only in ancient poetry and records of law, but also in compounds (byggja sifjar means "to marry"). Using this etymology, scholar John Lindow gives the meanings "in-law-relationship", scholar Andy Orchard provides "relation", and scholar Rudolf Simek gives "relation by marriage".
