'phototactic' originates from Greek, specifically the combining elements 'phōt-' (from 'phōs') meaning 'light' and 'taxis' meaning 'arrangement, order, or directed movement'.

'phototactic' was formed in Modern English (late 19th century) by combining the prefix 'photo-' (from Greek 'phōs') with the combining form '-tactic' (from Greek 'taktikos' / noun 'taxis'), producing a term describing movement/orientation related to light.

Initially built from roots meaning 'light' + 'arrangement/movement', it has come to be used specifically for organisms or responses that show phototaxis — directed movement or orientation in response to light.