Idioms start with letter [A]

[[Thamer]]

A Bird In The Hand Is Worth Two In The Bush:
Having something that is certain is much better than taking a risk for more, because chances are you might lose everything.

A Blessing In Disguise:
Something good that isn't recognized at first.

A Chip On Your Shoulder:
Being upset for something that happened in the past.

A Dime A Dozen:
Anything that is common and easy to get.

A Doubting Thomas:
A skeptic who needs physical or personal evidence in order to believe something.

A Drop in the Bucket:
A very small part of something big or whole.

A Fool And His Money Are Easily Parted:
It's easy for a foolish person to lose his/her money.

A House Divided Against Itself Cannot Stand:
Everyone involved must unify and function together or it will not work out.

A Leopard Can't Change His Spots:
You cannot change who you are.

A Penny Saved Is A Penny Earned:
By not spending money, you are saving money (little by little).

A Picture Paints a Thousand Words:
A visual presentation is far more descriptive than words.

A Piece of Cake:
A task that can be accomplished very easily.

A Slap on the Wrist:
A very mild punishment.

A Taste Of Your Own Medicine:
When you are mistreated the same way you mistreat others.

A Toss-Up:
A result that is still unclear and can go either way.

Actions Speak Louder Than Words:
It's better to actually do something than just talk about it.

Add Fuel To The Fire:
Whenever something is done to make a bad situation even worse than it is.

Against The Clock:
Rushed and short on time.

All Bark And No Bite:
When someone is threatening and/or aggressive but not willing to engage in a fight.

All Greek to me:
Meaningless and incomprehensible like someone who cannot read, speak, or understand any of the Greek language would be.

All In The Same Boat:
When everyone is facing the same challenges.

An Arm And A Leg:
Very expensive. A large amount of money.

An Axe To Grind:
To have a dispute with someone.

Apple of My Eye:
Someone who is cherished above all others.

As High As A Kite:
Anything that is high up in the sky.

At The Drop Of A Hat:
Willing to do something immediately.

[Anglika]

English Idioms and Idiomatic Expressions - UsingEnglish.com

[mfwills]

As High As A Kite:
Anything that is high up in the sky.

Literally, yes.

Idiomatically, it describes someone who is seriously under the influence of a given substance (typically not alcohol). Less frequently, I have heard it used to describe someone who is in an exceptionally good mood.

[mfwills]

Additionally, I tend to take issue with the first eleven examples, simply because the initial "A" indicates only a single occurrence of the expression, not the first letter of a significant word as in the other examples.