'astrophotometry' originates from modern English, formed from the Greek-derived prefix 'astro-' (from Greek 'astron' meaning 'star'), 'photo-' (from Greek 'phōs/phot-' meaning 'light'), and the suffix '-metry' (from Greek 'metron' meaning 'measure').

'astrophotometry' developed as a compound by adding the prefix 'astro-' to 'photometry' (the latter coming via New/Modern Latin and Greek roots for 'light' and 'measure') during the late 19th to 20th century, as photographic and electronic techniques in astronomy became established; the combined term entered English usage in the 20th century.

Initially the root elements referred broadly to 'measurement of light'; over time the compounded term came to mean specifically the measurement of the brightness of celestial objects.