In a horse race when the horses are neck in neck, the horse who won just won by putting his/her nose up just a little bit farther than the other. 'Win by a nose' means that the win was a very close one.
It comes from horseracing, and it just means "by a little bit" ... more than "by a hair," but less than "by a mile."
To poke your nose into is to insert yourself into someone else's business.
From horse racing, where they judge the winner of the race by which horse's nose crosses the line first.
It is not an idiom, it means your nose is itching.
If something is under your nose, you'd see it, right? It means that something is right there, in plain sight, obvious to everyone.
An idiom is a phrase that makes no sense unless you know the definition. Can a nose actually run somewhere? No, so this is an idiom.
A British police euphemism meaning to keep out of trouble, commit no crimes
"To be" is not an idiom - it's a verb.
The Idiom actually reads 'Fighting tooth and Nail'. It means to give everything you've got, literally every tooth and nail in your body, to win a struggle.
say no to it
Sometimes we are looking for something 10 or 100 feet away and it is right at our feet and don't see it, hence, 'right "under your nose"'.Something that is under someone's nose is something that the person is seeking that is right in front of him/her.
Pest is not an idiom. It's a word.
Doing anything "by a hair" means that you barely manage it. If you win by a hair, you win only by the margin as wide as a hair is. If you lose by a hair, you almost won. You can also have a "close shave," which is an idiom meaning that you escaped something bad by a hair's width.