滑
カツ, コツ, すべ.る, なめ.らか, かり, なめり

slippery, slide, slip, flunk

JLPT1 G7 S13 F1238

As per 骨# (circulate) + 水 water. However, as the character bears the primary meanings*slip*, *slide*, *glide* and *skate*, it is likely that 水 was originally 氷 ice, with the term originally signifying "glide/skate in a circle." Associated and extended meanings include *ski* and *smooth*, along with *fail* and *be demoted* (← slip up and pay the consequences).

[Full Kanji Etymology List]