–adjective

1.	(of books, usually children's books) having pieces of artwork fastened to the pages so that when the page is opened, a three-dimensional cutout or object is formed and, sometimes, movement of a picture element, such as a door opening, can be activated by pulling a tab.

2.	of or being a device that ejects or raises a finished or used item from the top: a pop-up toaster.

3.	of or pertaining to a device, mechanism, or object that rises or pivots from a concealed or recessed position to its operating position: a camera with a pop-up electronic flash; a car with pop-up headlights.

4.	popping up, as from an appliance or object: pop-up waffles heated in the toaster; a pop-up gauge for indicating when the turkey is done.

–noun

5.	a pop-up book.

6.	something, as a partially cut out or spring-mounted illustration in a children's book, that unfolds or springs up when opened or otherwise activated; pop-out: a Christmas card with a pop-up of Santa Claus.

7.	Baseball. pop fly.

–noun

1.	any substance, as cloth, paper, porous porcelain, or a layer of charcoal or sand, through which liquid or gas is passed to remove suspended impurities or to recover solids.

2.	any device, as a tank or tube, containing such a substance for filtering.

3.	any of various analogous devices, as for removing dust from air or impurities from tobacco smoke, or for eliminating certain kinds of light rays.

4.	Informal. a filter-tipped cigarette or cigar.

5.	Photography. a lens screen of dyed gelatin or glass for controlling the rendering of color or for diminishing the intensity of light.

6.	Electronics, Physics. a circuit or device that passes certain frequencies and blocks others.

7.	Mathematics. a collection of subsets of a topological space, having the properties that the intersection of two subsets in the collection is a 7f subset in the collection and that any set containing a subset in the collection is in the collection.

–verb (used with object)

8.	to remove by the action of a filter.

9.	to act as a filter for; to slow or partially obstruct the passage of: The thick leaves filtered the sunlight.

10.	to pass through or as through a filter.

–verb (used without object)

11.	to pass or slip through slowly, as through an obstruction or a filter: Enemy agents managed to filter into the embattled country.

–verb (used without object)

1.	to break without complete separation of parts; become fissured: The plate cracked when I dropped it, but it was still usable.

2.	to break with a sudden, sharp sound: The branch cracked under the weight of the snow.

3.	to make a sudden, sharp sound in or as if in breaking; snap: The whip cracked.

4.	(of the voice) to break abruptly and discordantly, esp. into an upper register, as because of weariness or emotion.

5.	to fail; give way: His confidence cracked under the strain.

6.	to succumb or break down, esp. under severe psychological pressure, torture, or the like: They questioned him steadily for 24 hours before he finally cracked.

7.	Chemistry. to decompose as a result of being subjected to heat.

8.	Chiefly South Midland and Southern U.S. to brag; boast.

9.	Chiefly Scot. to chat; gossip.

–verb (used with object)

10.	to cause to make a sudden sharp sound: The driver cracked the whip.

11.	to break without complete separation of parts; break into fissures.

12.	to break with a sudden, sharp sound: to crack walnuts.

13.	to strike and thereby make a sharp noise: The boxer cracked his opponent on the jaw.

14.	to induce or cause to be stricken with sorrow or emotion; affect deeply.

15.	to utter or tell: to crack jokes.

16.	to cause to make a cracking sound: to crack one's knuckles.

17.	to damage, weaken, etc.: The new evidence against him cracked his composure.

18.	to make mentally unsound.

19.	to make (the voice) harsh or unmanageable.

20.	to solve; decipher: to crack a murder case.

21.	Informal. to break into (a safe, vault, etc.).

22.	Chemistry. to subject to the process of cracking, as in the distillation of petroleum.

23.	Informal. to open and drink (a bottle of wine, liquor, beer, etc.).

–noun

24.	a break without complete separation of parts; fissure.

25.	a slight opening, as between boards in a floor or wall, or between a door and its doorpost.

26.	a sudden, sharp noise, as of something breaking.

27.	the snap of or as of a whip.

28.	a resounding blow: He received a terrific crack on the head when the branch fell.

29.	Inform 108 al. a witty or cutting remark; wisecrack.

30.	a break or change in the flow or tone of the voice.

31.	Informal. opportunity; chance; try: Give him first crack at the new job.

32.	a flaw or defect.

33.	Also called rock. Slang. pellet-size pieces of highly purified cocaine, prepared with other ingredients for smoking, and known to be especially potent and addicting.

34.	Masonry. check1 (def. 41).

35.	a mental defect or deficiency.

36.	a shot, as with a rifle: At the first crack, the deer fell.

37.	a moment; instant: He was on his feet again in a crack.

38.	Slang. a burglary, esp. an instance of housebreaking.

39.	Chiefly British. a person or thing that excels in some respect.

40.	Slang: Vulgar. the vulva.

41.	Chiefly Scot. conversation; chat.

42.	British Dialect. boasting; braggadocio.

43.	Archaic. a burglar.

–adjective

44.	first-rate; excellent: a crack shot.

–adverb

45.	with a cracking sound.

—Verb phrases

46.	crack down, to take severe or stern measures, esp. in enforcing obedience to laws or regulations: The police are starting to crack down on local drug dealers.

47.	crack off, to cause (a piece of hot glass) to fall from a blowpipe or punty.

48.	crack on, Nautical. a. (of a sailing vessel) to sail in high winds under sails that would normally be furled. b. (of a power vessel) to advance at full speed in heavy weather.

49.

crack up, Informal. a. to suffer a mental or emotional breakdown. b. to crash, as in an automobile or airplane: He skidded into the telephone pole and cracked up. c. to wreck an automobile, airplane, or other vehicle. d. to laugh or to cause to laugh unrestrainedly: That story about the revolving door really cracked me up. Ed cracked up, too, when he heard it.

—Idioms

50.	crack a book, Informal. to open a book in order to study or read: He hardly ever cracked a book.

51.	crack a smile, Informal. to smile.

52.	crack wise, Slang. to wisecrack: We tried to be serious, but he was always cracking wise.

53.	fall through the cracks, to be overlooked, missed, or neglected: In any inspection process some defective materials will fall through the cracks. Also, slip between the cracks.

54.	get cracking, Informal. a. to begin moving or working; start: Let's get cracking on these dirty dishes! b. to work or move more quickly.