At each other's throats
At ease
At every turn
At face value
At fault
At first
At first blush
At hand
At heart
At home
At it again
At large
At last
At least
At length
At loggerheads with (someone)
At loose ends
At odds (with someone)
At once
At one sitting
At one time
At one with (someone)
At one's fingertips
At one's heels
At one's wit's end
At peace
At random
At risk
At sea
At sea (about something)
At sixes and sevens
At stake
At the appointed time/hour
At the bottom of the hour
At the bottom of the ladder
At the crack of dawn
At the drop of a hat
At the eleventh hour
At the end of one's rope
At the end of the day
At the expense of (someone or something)
At the hands of (someone or something)
At the latest
At the mercy of (the court/someone)
At the present time
At the top of one's lungs
At the top of the hour
At this juncture
At this stage of the game
At times
At will
Attend to (someone or something)
Attract (someone's) attention
Attracted to (someone)
Augur well for (someone or something)
Avail oneself of (something)
Avenue of escape
Avoid (someone or something) like the plague
AWOL
B
B&B
B&E
BA
Back and forth
Back down
Back down (from someone or something)
Back in circulation
Back of beyond
Back on one's feet
Back out (of something)
Back the wrong horse
Back to basics
Back to square one
Back to the drawing board
Back to the salt mines
Back up (someone or something)
Back-to-back
Bad blood (between people)
Bad egg
Bad hair day
Bad-mouth (someone or something)
Bad/rotten apple
Badger (someone)
Bag of tricks
Bail (someone or something) out
Bail (someone) out
Bail a company out
Bail out (of something)
Balance the books/accounts
Ball is in (someone's) court
Ball of fire
Ball park figure/estimate
Ballpark estimate/figure
Balls of one's feet
Bang for the buck
Bang/beat one's head against the wall
Bank on (someone or something)
Banker's hours
Bankroll someone
Baptism of fire
Bare bones (of something)
Bargain for (something)
Bargain on (something)
Barge in on (someone or something)
Bark is worse than one's bite
Bark up the wrong tree
Base one's opinion on (something)
Bat a thousand
Bat out of hell
Bats in the belfry
Batten down the hatches
Bawl out (someone)
Be a new one on (someone)
Be all ears
Be all things to all people
Be at one's wit's end
Be cricket
Be curtains for (someone or something)
Be dealt a bad hand/deal someone a bad hand