senescence sih-NEH-sun(t)s, noun:
The state of being old; the process of growing old; aging.

Senescence is from Latin senescere, “to grow old,” from senex, “old.” It is related to senile. The adjective form is senescent.

thegosis THE-go-sis noun

Grinding of teeth as a means of sharpening them.

From Greek thegos, to sharpen.

(Bruxism is the word for night-time grinding of teeth.)