私信

私信	sī xìn	private correspondence; personal letter / (computing) personal message (PM); to message sb
私	sī	(bound form) personal; private / (bound form) selfish / (bound form) clandestine / (bound form) illicit / (Internet slang) to send a private message to sb
信	xìn	letter / mail / CL:封 / to trust / to believe / to profess faith in / truthful / confidence / trust / at will / at random