knock

1. knock Noun. (automotive) preignition|Preignition, a type of abnormal combustion occurring in spark ignition engines caused by self-ignition or the characteristic knocking sound associated with it.
preignition
1. Noun. (automotive) The premature detonation of a fuel charge in w:four-stroke cycle|Four-stroke cycle engines.
2. Noun. (automotive) The premature detonation of a fuel charge in w:four-stroke cycle|Four-stroke cycle engines.
abnormal
1. Adjective. Not conforming to rule or system; deviating from the usual or normal type. (defdate|First attested around the mid 19th century.)(reference-book | last =| first = | authorlink = | coauthors = | editor =Brown, Lesley | others = | title = The Shorter Oxford English Dictionary | origdate = | origyear = 1933| origmonth = | url = | format = | accessdate = | accessyear = | accessmonth = | edition = 5th | date = | year =2003| month = | p
2. Adjective. Of or pertaining to that which is abnormal, in particular, behaviour that deviates from norms of social propriety or accepted standards of mental health. (defdate|First attested around the early 20th century.)
3. Noun. A person or object that is not normal.
combustion
1. Noun. (chemistry) The act or process of burning.
2. Noun. A process where two chemicals are combined to produce heat.
3. Noun. A process wherein a fuel is combined with oxygen, usually at high temperature, releasing heat.
4. Noun. (figuratively) Violent agitation, tumult.
Sound
1. Proper noun. The strait that separates Zealand (an island of Denmark) from Scania (part of Sweden); also sometimes called by the Danish name, ├śresund.
sound
1. Adjective. healthy|Healthy.
2. Adjective. complete|Complete, solid, or secure.
3. Adjective. (mathematics|logic) (argument|logical system) having the soundness property.
4. Adjective. (British|slang) Good.
5. Adjective. (of sleep) quiet|Quiet and deep. (non-gloss definition|''sound asleep|Sound asleep'' means ''sleeping peacefully, often deeply''.)
6. Adverb. Soundly.
7. Interjection. (British|slang) yes|Yes; used to show agreement or understanding, generally without much enthusiasm.
8. Noun. A sensation perceived by the ear caused by the vibration of air or some other medium.
9. Noun. A vibration capable of causing this.
10. Noun. (music) A distinctive style and sonority of a particular musician, orchestra etc
11. Noun. Noise without meaning; empty noise.
12. Verb. (intransitive) To produce a sound.
13. Verb. (intransitive|copulative) To convey an impression by one's sound.
14. Verb. (intransitive|legal) To arise or to be recognizable as arising within a particular area of law.
15. Verb. (transitive) To cause to produce a sound.
16. Verb. (phonetics) To pronounce a vowel or a consonant.
17. Noun. (geography) A long narrow inlet, or a strait between the mainland and an island; also, a strait connecting two seas, or connecting a sea or lake with the ocean.
18. Verb. (intransitive) dive downwards, used of a whale.
19. Verb. To ascertain, or try to ascertain, the thoughts, motives, and purposes of (a person); to examine; to try; to test; to probe.
20. Verb. test; ascertain the depth of water with a sounding line or other device.
21. Verb. (medicine) To examine with the instrument called a sound, or by auscultation or percussion.
22. Noun. A long, thin probe for sound#Verb|sounding body cavities or canals such as the urethra.
23. Noun. The air bladder of a fish.
24. Noun. A cuttlefish.