TWO PRONUNCIATIONS

Two pronunciations, two meanings,
One spelling there be;
When I'm discovered, a heteronym you'll see.
My first can be gentle, but also can bite,
Felt and heard, but out of our sight.
To fix clocks or string, if you have the notion,
My second you'll need - it's a circular motion.

Answers:

WIND as in "The wind is blowing." and 
WIND as in "You have to wind the watch to keep it running."