'subgiant' originates from the Latin prefix 'sub-' (from Latin 'sub' meaning 'under') combined with the word 'giant' (from Old French 'geant', from Late Latin 'gigans', from Greek 'gigas' meaning 'giant').

'subgiant' arose in modern English as a compound of 'sub-' + 'giant', adopted into astronomical vocabulary in the 19th–20th century to name a star class between main-sequence and giant stars.

Initially the parts literally meant 'under' + 'giant' (i.e., 'less than a giant'); over time the term came to denote the specific evolutionary stellar stage now called 'subgiant'.