私通

私通	sī tōng	to have secret ties with / to be in covert communication with (the enemy etc) / to engage in an illicit sexual relationship / adultery
私	sī	personal / private / selfish
通	tōng	to go through / to know well / (suffix) expert / to connect / to communicate / open / to clear / classifier for letters, telegrams, phone calls etc
通	tòng	classifier for an activity, taken in its entirety (tirade of abuse, stint of music playing, bout of drinking etc)