Manner of speaking that is usual to native speakers of a language

He had to eat humble pie
To apologise humbly

He had to eat his words
To take back what you said

I found it difficult to make both ends meet
To live within my income

He turned a deaf ear to my suggestion
Disregarded

He will reach his goal by hook or by crook
By fair or foul means

Many people in Africa live from hand to mouth
Without any provision for the future

My friend burnt his fingers by partnering with him
Got himself into trouble

I strained every nerve to get him a job
Used his utmost efforts

The police said that the man had his finger in the pie
Has something to do with the affair.

Today my boss is in high spirits
Cheerful

What happened? You look out of spirits
(Sad)

She is not in my good books
In favour of

He has too many irons in the fire
Doing so many enterprises at a time

The Minister was murdered in cold blood
Deliberately

Evil elements must be nipped in the bud
To destroy before it grows

A Doubting Thomas
A person who doubts always

A leopard can't change his spots
It is not easy to change one’s nature.

Apple of my eye
Often daughters or sons are referred to as the "apple" of their parent's eye.

Back seat driver
The one who gives unnecessary advice.
This idiom comes from the habit many people have of giving too much advice (unwanted advice) to the driver of an automobile from the backseat.

Back to square one
Back to the beginning, to start again

Blind leading the blind
It is meant that the person in charge of the situation knows no more about it than those whom he is leading.

Blue Moon
The term Blue Moon means something that happens rarely, as in "once in a blue moon".

Catch-22
A situation in which a desired outcome or solution is impossible to attain because of a set of inherently illogical rules or conditions

Devil's Advocate
Devil’s advocate has come to mean a person who takes a position for the sake of argument. This practice is generally an instruction technique, whereby one person more experienced teaches another more novice to argue properly, taking in mind a position the latter doesn't know well or at all. This way, the depth of perspective of the arguer-to-be increases.

Don't look a gift horse in the mouth
When given something don't be ungrateful.
By counting the teeth you can tell the age of a horse.
Checking whether a present of a horse was old would be considered impolite.

Get out of the wrong side of the bed
Meaning to be in a bad mood, it is considered unlucky to put your left foot on the floor first when getting out of bed.

Good Samaritan
A good Samaritan is one who helps another in a time of need with no thought of reward.

Mum's the word
The humming sound made when a mouth is closed. This idiom means say nothing and keep your mouth shut.

My brother's keeper
Am I my brother’s keeper?’ means ‘I am not responsible for somebody’s action’.

Rain Cats and Dogs
Rain very hard.

Scapegoat
A scapegoat is someone who gets the blame for a scandal/mistake; typically, the scapegoat is either completely innocent, or at least is only one of many guilty people

Skin of Your Teeth
This saying means to barely escape from a harrowing situation.

Straight from the horse's mouth
Directly from the source; firsthand

Tongue in Cheek
Not intended seriously or humorous

Uncle Sam – is the government of USA

At the eleventh hour
At the last minute; almost too late.

A piece of cake
Be very easy

Beat around the bush
Evade an issue; avoid giving a direct answer.

Beat one's brains out
Try very hard to understand or do something.

Blabbermouth
A very talkative person--especially one who says things that should be kept secret.

Burn the midnight oil
Study/work all night or until very, very late at night.

Call it a day : stop work for the day.

Can’t make heads or tails of something
Can’t understand something at all; find something confusing and illogical.

Cool it !: calm down

Crash course
Short course designed to give a lot of knowledge/information in a very short time.

Don't count your chickens until they hatch
Don't assume that something will happen until it has happened.

Far-fetched
Difficult to accept; difficult to believe.

Hard feelings
Anger; animosity; bitter feelings.

Keep one's fingers crossed
Hope for the best.

A know-it-all
Someone who acts as if he/she knows everything

A white lie
A lie that is told to avoid offending someone or hurting his / her feelings