Hard Riddles for Adults

A station clock, a chess clock and a stopwatch all measure me, yet none can keep me once I have gone. What am I?

A gardener makes me larger by taking soil away, not by adding anything. What am I?

Shout one word into a tunnel and I return that word late, weaker, and with no idea what it means. What am I?

At midnight I may be tomorrow; by breakfast I have a new name. You can schedule me, but you can never arrive while I am still ahead. What am I?

The same photograph can make a crowd look huge or tiny, depending on which edges are cut away. What silent trick changed the truth?

The more kitchens copy me, the more meals I can make; hide me in a drawer and I feed nobody. What am I?

In a debate I may be made, missed, sharpened, or conceded, though I have no metal tip. What am I?

I arrive as a locked question with all the keys hidden in the clues. Solving me means arranging what is already there. What am I?

I may look awkward as 48 over 64, but the more you break me down by common factors, the clearer I become. What am I?

I sit in a corner, get cancelled before the journey begins, and may cross oceans stuck to someone else's words. What am I?

Feed me dry wood and air and I grow; starve me of oxygen or give me water and I die. What am I?

In wallpaper I am seen, in a drumbeat I am heard, and in a password I am hunted. Once noticed, I am hard to unsee. What am I?

I am first in end, last in place, and appear twice in experience. What am I?

A diver feels me in deep water, a student before an exam, and a tyre when it is inflated. Too much of me can crush. What am I?

No hands are needed to break me, no box can hold me, and keeping me matters only after I have been tested. What am I?

A bank studies me before lending, a writer wants me after a quotation, and a card can run out of me at the worst moment. What am I?

Lawyers build me, logicians test me, and one weak premise can make me collapse. What am I?

I sit under a conclusion so quietly that people may argue above me for hours. Challenge me, and the whole discussion can change. What am I?

A fence may mark me, a deadline may become me, and a joke may reveal me only after it has gone too far. What am I?

A referee gives me, a court records me, and a crowd may pass me before the evidence is complete. What am I?

It leaves no bruise, yet one remembered action can make it grow heavier for years. What is it?

A sunflower head, a pine cone spiral and the numbers 1, 1, 2, 3, 5 all point to me. What am I?

I can stop a sale, protect a boundary, end a request, or save a life. I am only two letters. What word am I?

Two identical glasses hide me. Fill one a centimetre higher than the other, and I appear. What am I?

At a border I may be crossed; in a queue I may be joined; in a script I may be delivered. Same word, three places. What am I?

The moment I am told, I still exist, but I no longer belong to one person. Add more keepers and I become harder to keep. What am I?

I tell time by copying the sun's refusal to stand still; indoors I am useless, and at noon I almost disappear. What am I?

Move me one place in an invoice and ten pounds becomes a hundred; I look tiny, but I can empty a budget. What am I?

Evidence can open me, fear can close me, and one conversation can change me without touching me. What am I?

I am not written on a CV; comfort may hide me, pressure reveals me, and repeated choices build me slowly. What am I?

A detective may reach me without taking a step, and one false clue can send me in the wrong direction. What am I?

A coin is a circle on the table, an oval from the side, and almost a line at eye level. What changed?

Project managers like me broken into tasks; ignored, I grow costlier; examined, I reveal the next step. What am I?

A camera needs me before the picture is sharp; a meeting loses me when every phone starts buzzing. What am I?

A lawyer builds me with facts, doubt weakens me, and proof can make me strong again. What am I?

I begin with two premises and end with a conclusion; if my middle term fails, so do I. What am I?

Scientists trust me only after trying to prove me wrong; assume me without testing and I am just a guess. What am I?

You can count along me, divide me, make me negative, and still never reach my final member. What am I?

Eight is correct after five plus three, wrong after five times three, and meaningless on a blank page. What am I?

I find cracks before publication, improve an argument by pressing its weak points, and work best when the attack is fair. What am I?

Write me in a diary and I am ahead of you; wake up inside me and everyone calls me today. What am I?

Ten seconds before midnight I make a room loud; ten seconds before an exam I make it silent. Same numbers, different feeling. What am I?

I arrive slowly through kept promises, leave quickly after one public lie, and often enter the room before you do. What am I?

A violin string needs enough of me to sing; a room after an argument can have too much of me, even in silence. What am I?

Court records, photographs and scars can show me. Apologies may change my meaning, but not my events. What am I?