'athetotic' originates from the medical noun 'athetosis', ultimately from Greek 'athētos' (ἀθέτος) meaning 'displaced, without position' (from a- 'without' + thetos/ from tithemi 'to place').

'Athetosis' was coined in the 19th century in medical literature (described by William A. Hammond in 1871); 'athetotic' was later formed in English as the adjective derived from that noun.

Initially the Greek root conveyed the sense 'without a fixed place/position'; in medical English it evolved to denote the specific disorder of slow, writhing involuntary movements, and 'athetotic' now describes things relating to that condition.