a period of indeterminate length (usually short) marked by some action or condition; "he was here for a little while"; "I need to rest for a piece"; "a spell of good weather"; "a patch of bad weather"
based on custom rather than documentation; "an unwritten law"; "rites...so ancient that they well might have had their unwritten origins in Aurignacian times"- J.L.T.C.Spence