NISI Meaning of NISI in English [ 'nʌɪsʌɪ ]■ adjective [ postposition ] Law (of a decree, order, or rule) valid or taking effect only after certain conditions are met.OriginC19: from L., lit. 'unless'. Concise Oxford English vocab. Сжатый оксфордский словарь английского языка. 2004