Where does “giga-” come from?

giga- (Polish) comes from Ancient Greek Γίγας, from Ancient Greek Γίγᾱς.

Ancestry of “giga-”, step by step

Step	Language	Word	Meaning
1	Ancient Greek	Γίγας	one of the Gigantes; a Gigas
2	Ancient Greek	Γίγᾱς	—