A kestrel is a small hunting bird in the falcon family — much smaller than the big falcons people see in films. The thing you notice first is how it flies: it can face the wind and hang in one spot in the air, wings working, tail open, while it watches the grass for a mouse. Then it drops. Country people have always known this bird for that trick, even when they never learned the name. Kestrels also sit on roadside wires and poles, looking down. They eat mice, insects, and sometimes small birds, so farmers used to think of them as a friend of the field — though they are wild, not pets, and you do not keep one without a licence. The word covers several small falcons of this kind, not only one country; the common European one is often reddish-brown, and the male has a grey head. You say KESS-trul. It is a quiet nature word, not slang and not fancy.