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1.
Un - No or not.
tail - Regarding the devil's tail, representing evil.
(No-tail)
(No-evil)
(Not-evil)
1.) (No tail) meaning you do not represent evil.
2.) Someone against evil ways.
Ex.
Guy 1: Ay man you wanna join the illuminati?

Guy 2: No way man! Im with god, Im untail.
by New guy 23 March 06, 2013