Here’s a list to jog your memory.^[1]

A. Making Decisions
Sit on the fence – Avoid making a decision.
A bird in the hand is worth two in the bush – It's better to hold on to something you already have than risk losing it by seeking more.
Stick to your guns – Stay firm with your decision despite criticism.
Up in the air – No decision has been made yet.
In two minds – Unsure of what to choose or do.

B. Love & Relationships
Love at first sight – Falling in love instantly upon meeting.
Match made in heaven – A perfect couple.
Tie the knot – Get married.
Puppy love – Immature or adolescent romantic feelings.
Blinded by love – Unable to see flaws in someone due to love.
Play gooseberry – Be the unwanted third person with a couple.
Shotgun wedding – A rushed marriage due to an unplanned pregnancy.
Birds and bees – Euphemism for explaining sexual intercourse.
Village bicycle – Derogatory term for a promiscuous woman.

C. Secrets & Privacy
Behind closed doors – In secret or privately.
Cover your tracks – Hide evidence of your actions.
Fly on the wall – Secretly observe without being noticed.
Keep a low profile – Avoid attracting attention.
Keep under wraps – Keep something secret.
Skeleton in the closet – A hidden, shameful secret.
Sweep under the rug – Hide something embarrassing.

D. Growing Up / Challenges
Made a comeback – Returned to success after failure.
Bite the bullet – Endure hardship or face a tough situation.
Survive the test of time – Remain relevant or successful over time.
Survival of the fittest – Only the strong succeed or survive.
Tough it out – Persevere through difficulty.

E. Colour Idioms
Black sheep – A family member who is a disgrace.
Black out – To faint.
Blacklist – A list of banned people/items.
Black book – A list of secret contacts.
Black-tie event – A formal social gathering.
Black and white – Clear and straightforward.
Black and blue – Bruised.
Pass with flying colors – Do very well.
True colors – One’s real nature.
Be off-color – Slightly unwell or inappropriate.
Lend color to – Add details to make something believable.
Chase rainbows – Pursue unrealistic goals.
Golden opportunity – The best chance to do something.
Green light – Approval or permission.
Once in a blue moon – Very rarely.
White elephant – A costly, useless item.
With flying colours – Very successfully.
Yellow – Cowardly.
Feeling blue – Feeling sad.

F. Nature
Beat around the bush – Avoid the main topic.
A breath of fresh air – A welcome change.
Fan the flames – Make emotions stronger.
Add fuel to the fire – Make a bad situation worse.
Chasing rainbows – Pursue something unrealistic.
Calm before the storm – A peaceful moment before chaos.

G. Health & Medicine
Alive and kicking – Healthy and active.
Back on one’s feet – Recovered from illness.
One foot in the grave – Near death.
Green around the gills – Looking sick.
In the pink of health – In excellent health.
A dose of one’s own medicine – Receive the same bad treatment one gave.
A bitter pill to swallow – An unpleasant but necessary situation.

H. Science & Technology
Blow a fuse – Lose your temper.
Not rocket science – Not difficult to understand.
A well-oiled machine – Works efficiently and smoothly.
Pull the plug – Stop something from continuing.
On the same wavelength – Understand each other well.

I. Money
Penny wise, pound foolish – Save small amounts, waste large ones.
Money doesn’t grow on trees – Money is not easily obtained.
A fool and his money are soon parted – Careless people lose money quickly.
A penny saved is a penny earned – Saving money is as good as earning it.
The best things in life are free – Valuable things don’t always cost money.
Save for a rainy day – Save money for difficult times.

J. Sky & Moon Idioms
Aim for the sky – Set high goals.
Out of the clear blue sky – A complete surprise.
On cloud nine – Extremely happy.
Building castles in the air – Dreaming unrealistically.
Pie in the sky – Unrealistic hope or goal.
The sky’s the limit – Anything is possible.
Over the moon – Extremely happy.
All moonlight and roses – Idealistic but unrealistic.
Many moons ago – A long time ago.
To ask for the moon – Ask for the impossible.

K. Transport / On the Go
In the same boat – In the same difficult situation.
Take flight – Flee or run away.
Go off the rails – Behave in a wild or uncontrolled way.
Train of thought – A line of reasoning.
End of the road – The point where progress stops.

L. Birds
Birds of a feather flock together – Similar people stick together.
Chickens come home to roost – Bad deeds have consequences.
Like a duck takes to water – Do something naturally.
Albatross around one’s neck – A burden or problem.
A bird in the hand is worth two in the bush – Better to keep what you have.

M. Idioms from Daily Life
Trial and error – Experiment until something works.
Odds and ends – Small leftover items.
Said and done – Final conclusion or decision.
Back and forth – Moving between two places.
Ups and downs – Good times and bad times.
Wine and dine – Entertain with lavish meals.
Spick and span – Very clean and tidy.
Ins and outs – Full details.
Bread and butter – Main source of income.

N. Others / Pop Culture / Humour
Kick the bucket – Die.
The bee’s knees – Excellent.
Blur like sotong – Clueless or confused.

1. Yes, I prepared it for my fifth graders ↩