けつ

From Middle Chinese 穴 (MC hwet).

けつ • (ketsu) 

1. (informal) ass; arse; buttocks

   ケツの穴(あな) ― ketsu no ana ― anus; butthole

2. (informal) last or hindermost part

   けつから五(ご)番(ばん)目(め) ― ketsu kara gobanme ― fifth last

3. (informal) upcoming item on the schedule

   この後(あと)ケツがある

   kono ato ketsu ga aru

   have something scheduled after this

4. (informal) gay sex, sex between two men

• Almost never written as kanji 穴, perhaps to avoid ambiguity with 穴(あな) (ana).

(The following entries are uncreated: 決, 欠.)