Via Simon Roberts in email:
"The meaning of a word is not a matter of fact (which is why an argument about it can't be settled by recourse to the dictionary), and it is not a matter of opinion (which is why an argument about it mustn't be unsettled by a refusal to have recourse to the dictionary). The meaning of a word is a human agreement, created within society but incapable of having meaning except to and through individuals. We may find evidence for such agreements, but we can't find proof of them. A language is a body of agreements. Some lapse; others change; new ways form".
(From The State of Language (Ricks).)