: reflex translational or orientational movement by a freely motile and usually simple organism in relation to a source of stimulation (such as a light or a temperature or chemical gradient)
borrowed from German Taxis, borrowed from Greek táxis "drawing up in rank and file, order of battle, arrangement, order," from tag-, stem of tássein (Attic táttein) "to draw up in order (as troops, ships), post, station, place in order, prescribe, assess" + -sis-sis — more at tactic entry 2
Noun combining form
borrowed from Greek táxis "arrangement, disposition, order" — more at taxis