'aphotactic' is a modern formation from the negative prefix 'a-' + 'photactic' (from 'phototaxis'), ultimately from Greek 'phōs' or 'phōt-' meaning 'light' and 'taxis' meaning 'arrangement' or 'ordering'.

'phototaxis' comes from Greek 'phōs/phōt-' ('light') + 'taxis' ('arrangement, order'); it produced the adjective 'phototactic' in scientific use, and the negative prefix 'a-' was later attached to form 'aphotactic' meaning 'not phototactic'.

Originally referring to the concept of 'lack of directed movement in relation to light', the word has retained that technical biological meaning in modern usage.