Here is a list of idiomatic expressions built around words beginning with A.
Take someone aback
To take someone aback is to shock or surprise them.
He looked taken aback.
Abandon yourself to
To abandon yourself is to give in to something completely.
If you cannot abide something, you dislike it very much.
Be about to
When you are about to do something, you are on the point of doing it.
Of your own accord
When you do something off your own accord, you are doing it willingly.
Call someone to account
To call someone to account is to ask them to explain poor performance.
On account of
On no account
Under no circumstances
Take account of
To take account of something is to take that into consideration.
Ace up one’s sleeve
When you have an ace up your sleeve, you have a trick or piece of information that you keep secret until it is needed.
Act of God
An event caused by natural forces beyond human control
Get in on the act
To get in on the act is to become involved in something to share the profits.
Airs and graces
Pretentious behavior intended to impress people.
Up in the air
If an issue is up in the air, it is not yet resolved or settled.
Walk on air
You walk on air when you feel very happy or pleased.
All and sundry
To invite all and sundry is to invite everyone.
When you are all for something, you are strongly in favor of it.
When you are all in, you are exhausted.
On all fours
When you are on all fours, you are standing on your hands and legs.
Leave someone /something alone
To leave someone or something alone is to stop interfering with them.
Keep up appearances
To keep up appearances is to keep up an impression of well-being or wealth.
Cost an arm and a leg
If something costs an arm and a leg, it is very expensive.
Keep someone at arm’s length
To keep someone at arm’s length is to avoid close contact with them.
Up in arms
When you are up in arms, you are protesting about something vigorously.