knot (noun) [pronounce not] – a tie (of material or people)

knot (verb) – to tie into a knot

knotty (adjective) – complicated

David Merrett

Here are some examples of how you can use it:

These garbage bags have drawstrings that you can tie with a knot to close them.

The cat’s hairball (= the stuff they throw up) looks like a knot of hairs and leaves.

He was so worried that his stomach tied itself into a knot.

There was a knot of paparazzi at his doorstep waiting for him to come out.

Oh, you’re thirty already. Time to tie the marriage knot!

The fisherman knotted the rope tightly.

I don’t know how to solve this. Looks like a knotty problem.