**Involution** : function which is its own inverse

(e.g. If *f*(*x*) = *x*
/ (*x-*1), then *f*^{
-1}(*x*) = *x* / (*x-*1) = *f*(*x*).)

**Contronym** :
word which is its own opposite

(e.g. **fast**, which means moving quickly, as in “He ran fast.”, as well
as not

moving at
all, as in “He held fast.”)

http://en.wikipedia.org/wiki/Involution

http://mathworld.wolfram.com/Involution.html

http://en.wikipedia.org/wiki/Auto-antonym

http://www.rinkworks.com/words/contronyms.shtml

(nice list !!)