godan verb (-ru)
masturbate; jerk off
Slang term for male masturbation; very casual and direct. Not used in polite contexts.
昨日、久しぶりにシコった。
Yesterday, I jerked off for the first time in a while.
More clinical and gender-neutral term for masturbation, borrowed from German 'Onanie'. シコる is exclusively male and slangy.
Formal, clinical term. シコる is extremely informal and would never be used in medical or polite settings.
Slang coinage; likely derived from the sound-symbolic element シコシコ (shiko-shiko), which mimics a repetitive rubbing motion. The exact origin is uncertain.