From Greek Ἀρέθουσα (Arethousa) meaning “quick water”, which is possibly derived from ἄρδω (ardo) meaning “water” and θοός (thoos) meaning “quick, nimble”. This was the name of a nymph in Greek mythology who was transformed into a fountain.
From Japanese 茂 (shigeru) meaning “lush, luxuriant”, as well as other kanji having the same reading. A famous bearer is the Japanese video game designer Shigeru Miyamoto (1952-).