'galaxy-spanning' originates from English, specifically the compound of 'galaxy' and the present participle 'spanning', where 'galaxy' referred to a large system of stars and 'spanning' meant 'stretching across'.

'galaxy' comes from Greek 'galaxias' (via Latin 'galaxias'), ultimately from 'gala' meaning 'milk' (a reference to the Milky Way); 'span' derives from Old English 'spannan' (to stretch), through Middle English forms to modern 'span' and the participle 'spanning'.

Initially, 'galaxy' specifically referred to the Milky Way (a 'milky' band of stars) and 'span' simply meant 'to stretch across'; together the compound has come to mean both the literal idea of stretching across multiple galaxies and the figurative sense of extremely large scope.