[yesterday] See: BORN YESTERDAY.

[yon] See: HITHER AND THITHER or HITHER AND YON.

[yoo-hoo]{interj.}?—?Used as an informal call or shout to a person to attract his attention. •/Louise opened the door and called "Yoo-hoo, Mother?—?are you home?"/ See: ALL RIGHT FOR YOU, I’M TELLING YOU, SAYS WHO or SAYS YOU, THAT’S --- FOR YOU, WHAT HAVE YOU.

[you bet] or [you bet your boots] or [you bet your life] {informal} Most certainly; yes, indeed; without any doubt.?—?Used to declare with emphasis that a thing is really so. •/Do I like to ski? You bet your life I do./ •/You bet I will be at the party./ •/You can bet your boots that Johnny will come home when his money is gone./ Compare: BET ONE’S BOTTOM DOLLAR.

[you can say that again] See: YOU SAID IT.

[you can’t teach an old dog new tricks] It is very hard or almost impossible to train an older person to acquire some new skill.?—?A proverb. •/You’ll never teach your grandfather how to do his income tax on a personal computer. You can’t teach an old dog new tricks./

[you don’t say]{interj.}, {informal}?—?Used to show surprise at what is said. •/Your ring is a real diamond? You don’t say!/ •/"Bill and Jean are going to get married." "You don’t say!"/ Syn.: DO TELL.

[your] See: HANG ON TO YOUR HAT or HOLD ON TO YOUR HAT or HOLD YOUR HAT, YOU BET YOUR BOOTS or YOU BET YOUR LIFE.

[you’re telling me]{interj.}, {informal}?—?Used to show that a thing is so clear that it need not be said, or just to show strong agreement. •/"You’re late." "You’re telling me!"/ Compare: YOU BET, YOU SAID IT.

[you said it] or [you can say that again] {interj.}, {slang}?—?Used to show strong agreement with what another person has said. •/"That sure was a good show." "You said it!"/ •/"It sure is hot!" "You can say that again!"/ Compare: SAY A MOUTHFUL.

[you tell 'em]{interj.}, {slang}?—?Used to agree with or encourage someone in what he is saying. •/The drunk was arguing with the bartenders and a man cried, "You tell 'em!"/

[yours truly]{adv. phr.} 1. Signing off at the end of letters. •/Yours truly, Tom Smith./ 2. I, the first person singular pronoun, frequently abbreviated as t.y. •/As t.y. has often pointed out…/ •/T.y. is not really interested in the offer./

[yum-yum]{interj.}, {informal}?—?Used usually by or to children, to express great delight, especially in the taste of food. •/"Yum-Yum! That pie is good!"/

[zero hour]{n.} 1. The exact time when an attack or other military action is supposed to start. •/Zero hour for the bombers to take off was midnight./ 2. The time when an important decision or change is supposed to come; the time for a dangerous action. •/It was zero hour and the doctor began the operation on the man./ •/On the day of the championship game, as the zero hour came near, the players grew nervous./

[zero in on]{v.} 1. To adjust a gun so that it will exactly hit (a target); aim at. •/Big guns were zeroed in on the enemy fort./ •/American missiles have been zeroed in on certain targets, to be fired if necessary./ 2. {slang} To give your full attention to. •/The Senate zeroed in on the Latin-American problems./ •/Let’s zero in on grammar tonight./

[zip one’s lip] See: BUTTON ONE’S LIP.

[zone defense]{n.} A defense in a sport (as basketball or football) in which each player has to defend a certain area. •/The coach taught his team a zone defense because he thought his players weren’t fast enough to defend against individual opponents./

[zonk out]{v. phr.}, {slang} 1. To fall asleep very quickly. •/Can I talk to Joe??—?Call back tomorrow, he zonked out./ 2. To pass out from fatigue, or alcohol. •/You won’t get a coherent word out of Joe, he has zonked out./

[zoom in]{v. phr.} 1. To rapidly close in on (said of airplanes and birds of prey). •/The fighter planes zoomed in on the enemy target./ 2. To make a closeup of someone or something with a camera. •/The photographer zoomed in on the tiny colibri as it hovered over a lovely tropical flower./