Full Idea
There is no ancient Greek word for duty; the word 'deon' (the basis of 'deontology') means what one must do.
Gist of Idea
'Deon' in Greek means what one must do; there was no word meaning 'duty'
Source
Bernard Williams (Ethics and the Limits of Philosophy [1985], Ch. 1)
Book Reference
Williams,Bernard: 'Ethics and the Limits of Philosophy' [Fontana 1985], p.16
A Reaction
Presumably it covered compulsions which were not duties, such as the need to eat or drink. Greeks thought morally, but lacked a good moral vocabulary?
Related Idea
Idea 497 Be virtuous from duty, not from fear [Democritus (attr)]