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
marked by obliqueness or indirection in speech or conduct; "the explanation was circuitous and puzzling"; "a roundabout paragraph"; "hear in a roundabout way that her ex-husband was marrying her best friend"