Here are some idioms using shapes.
square meal = a big meal: "After all that travelling, we needed a square meal."
be back to square one = to be back to where you started: "I don't feel we're making any progress - we're back to square one."
look someone square in the eye = look at someone directly: "He looked me square in the eye and denied taking the money."
fair and square = completely fair: "We negotiated the deal fair and square."
square up to someone = to not be scared of dealing with someone or something difficult: "I'm glad you squared up to him in the meeting - you were definitely right!"
to be square = to be old-fashioned or boring: "She's so square - she hates doing anything fun!"
square it with someone = to get someone to agree to something: "I don't know if we can afford a car - we'll have to square it with the bank first."
a square peg in a round hole = something that doesn't fit: "He shouldn't be the boss - it would be like a square peg in a round hole."
spiral out of control = a situation that gets worse all the time: "Our costs are spiralling out of control - we have to save money."
vicious circle = a situation which makes itself worse, so that there is little chance of improvement: "The two sides are locked in a vicious circle of hatred."
go round in circles = to never get out of a situation: "I feel we're not getting anywhere - we're just going round in circles."
go full circle = to go the whole distance and arrive back in the same place: "The company has now gone full circle and has returned to its original core products."
move in the same circles = know the same people socially: "I'm afraid I don't know the Queen personally - we don't move in the same circles!"
in round figures = to the nearest unit: "In round figures, he earns 80 000 USD."
round something up or down to the nearest = give the closest even amount: "How much do we owe? Well, to round it up to the nearest dollar, I'd say about 60 USD."
the first time round = the first time that you did something: "Have you ever lived in London? Yes, the first time round, I was working in a school."
do the rounds = to be circulating: "There's a new joke doing the rounds about the President."
round on someone = to turn on someone: "She suddenly rounded on him and called him a liar."
a round of sandwiches = two sandwiches (made from two pieces of bread): "She made a few rounds of cheese sandwiches."
a round of golf = a game of golf: "Fancy a round of golf this evening?"
a round of drinks = a drink for everyone: "It's my turn to buy a round of drinks. What does everyone want?"