tick

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A light, sharp, clicking sound made repeatedly by a machine, such as a clock.
• noun Chiefly British A moment.
• noun A light mark used to check off or call attention to an item.
• noun Informal A unit on a scale; a degree.
• intransitive verb To emit recurring clicking sounds.
• intransitive verb To function characteristically or well.
• intransitive verb To count or record with the sound of ticks.
• intransitive verb To mark or check off (a listed item) with a tick.
• noun Credit or an amount of credit.
• noun Any of various small bloodsucking arachnids of the order Ixodida that are parasitic on terrestrial vertebrates. Many species transmit diseases, such as Rocky Mountain spotted fever and Lyme disease.
• noun Any of various usually wingless insects that resemble a tick, such as a sheep ked.
• noun A cloth case for a mattress or pillow.
• noun A light mattress without inner springs.
• noun Ticking.

from The Century Dictionary.

• noun A slight touch or tap; a pat.
• noun A slight sharp sound, as that made by a light tap upon some hard object; also, a recurring click or beat, as of a watch or clock.
• noun The game known in the United Kingdom as tig, and in the United States as tag. See tag.
• noun A dot or slight mark: as, the tick over the letter i; the tick used in checking off the items in a list or catalogue.
• noun A small spot or color- mark on the coat of an animal.
• noun A speck; a particle; a very small quantity.
• noun Credit; trust: as, to buy on tick.
• noun A score, account, or reckoning.
• To buy on tick or credit; live on credit.
• To give tick or credit; trust one for goods supplied, etc.
• To touch or tap something lightly, or with a small sharp sound; tap slightly, as a bird when picking up its food; peck.
• To emit a slight recurring click, like that of a watch or clock.
• To touch lightly, as in the game of tag or tig; tag.
• To place a dot on, over, or against; mark with or as with a tick or dot: as, to tick one's i's in writing; to set a dot against, as in checking off the items in a list or catalogue; check by writing down a small mark: generally with off.
• To note or mark by or as by the regular clicking of a watch or clock.
• noun The cover or case of a bed, which contains the feathers, hair, corn-shucks, moss, or other materials conferring softness and elasticity.
• noun Ticking.
• noun The whinchat.
• noun One of many different kinds of mites or acarines which are external parasites of various animals, including man.
• noun Hence With a qualifying term, a member of the dipterous family Hippoboscidæ.
• noun The tick-bean.
• noun In a horse, the malady or vice now called cribbing.

from the GNU version of the Collaborative International Dictionary of English.

• noun Credit; trust.
• intransitive verb To go on trust, or credit.
• intransitive verb To give tick; to trust.
• noun A quick, audible beat, as of a clock.
• noun Any small mark intended to direct attention to something, or to serve as a check.
• noun (Zoöl.), Prov. Eng. The whinchat; -- so called from its note.
• noun (Zoöl.) See Deathwatch.
• noun Any one of numerous species of large parasitic mites which attach themselves to, and suck the blood of, cattle, dogs, and many other animals. When filled with blood they become ovate, much swollen, and usually livid red in color. Some of the species often attach themselves to the human body. The young are active and have at first but six legs.
• noun Any one of several species of dipterous insects having a flattened and usually wingless body, as the bird ticks (see under bird) and sheep tick (see under sheep).
• noun a small bean used for feeding horses and other animals.
• noun (Bot.) a name given to many plants of the leguminous genus Desmodium, which have trifoliate leaves, and joined pods roughened with minute hooked hairs by which the joints adhere to clothing and to the fleece of sheep.
• intransitive verb To make a small or repeating noise by beating or otherwise, as a watch does; to beat.