male masturbation
Vulgar slang term for male masturbation. Compare まんずり (female masturbation).
See also: マンズリ
Apparently he masturbates every night.
Katakana spelling is sometimes used for emphasis or in informal writing.
Rare kanji form; it is rarely used.
The origin is uncertain. The first element せん may be from 千 (thousand) used as an intensifier, and ずり is likely from 擦り (rubbing).