"unwritten" in the adjective sense
1. unwritten
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
2. oral, unwritten
using speech rather than writing
"an oral tradition"
"an oral agreement"
3. ad-lib, spontaneous, unwritten
said or done without having been planned or written in advance
"he made a few ad-lib remarks"
Source: WordNet® (An amazing lexical database of English)
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