'supergiant' is a compound of the prefix 'super-' (from Latin 'super', meaning 'above' or 'beyond') and 'giant' (from Old French 'geant' < Late Latin/Greek 'gigas', meaning 'giant').

'giant' comes from Greek 'gigas' (γίγας) via Late Latin and Old French into Middle English as 'giant'; 'super-' is from Latin 'super'. The compound 'supergiant' was coined in modern English (early 20th century) in astronomical usage to denote stars much larger and brighter than ordinary giants.

Originally formed by combining an intensifying prefix and 'giant' to mean 'above/very giant'; in astronomy it came to denote a specific stellar luminosity/mass class (very massive, very luminous stars) and has retained that technical sense while occasionally appearing in figurative uses.