3K

Etymology 1
Kitsui (きつい difficult, demanding), kitanai (汚い dirty) and kiken (危険 dangerous).

Noun

 * 1)  3D jobs

Etymology 2
Kitsui (きつい difficult, hard), kaerenai (negative potential of ), kyuryō ga yasui

Noun

 * 1)  a job that is hard, has long hours, and doesn't pay well