'astrologaster' originates from modern English, formed by combining 'astrologer' and the pejorative suffix '-aster', where '-aster' meant 'an inferior or pretended person'.

'astrologaster' was modeled on earlier English formations such as 'poetaster' (from Latin/English usage of the suffix '-aster'); 'astrologer' itself comes from Latin/Greek ('astrologus' from Greek 'astrologos', from 'astron' meaning 'star' + 'logos' meaning 'word/study').

Originally built from elements meaning 'student/speaker of the stars', the combined form came to mean specifically a 'pretender or inferior practitioner of astrology' rather than a legitimate student of the stars.