Where does “Gus” come from?

Gus is a shortened form of Augustus, which derives from Latin augustus meaning "majestic," itself from Latin augeo meaning "to increase," ultimately tracing to Proto-Indo-European h₂ewg-.

Ancestry of “Gus”, step by step

Step	Language	Word	Meaning
1	Swedish	Gustav	—
2	Old Swedish	Gøtstaf	—
3	Old Norse	Gautstafr	—
4	Old Norse	stafr	staff
5	Proto-Norse	ᛋᛏᚼᛒᚼ	—
6	Proto-Germanic	stabaz	staff, stick
7	Proto-Indo-European	stebʰ-	to stand still; to harden

Every word from Proto-Indo-European stebʰ- →