Real Dictionary

tick
countable noun: A tick is a written mark like a V: ✓. It is used to show that something is correct or has been selected or dealt with.
verb: If you tick something that is written on a piece of paper, you put a tick next to it.
verb: When a clock or watch ticks, it makes a regular series of short sounds as it works.

tick in American English 1
a light touch; pat
to make a tick or series of ticks, as a clock
intransitive verb: to emit or produce a tick, like that of a clock
noun: a slight, sharp, recurring click, tap, or beat, as of a clock
transitive verb: to sound or announce by a tick or ticks

tick in American English 2
credit; trust
noun: any of numerous bloodsucking arachnids of the order Acarina, including the families Ixodidae and Argasidae, somewhat larger than the related mites and having a barbed proboscis for attachment to the skin of warm-blooded vertebrates: some ticks are vectors

tick in American English 3
any of a superfamily (Ixodoidea, order Parasitiformes) of wingless, bloodsucking mites, including many species that transmit diseases and are usually parasitic on humans, cattle, sheep, etc.
noun: the cloth case of a mattress, pillow, etc., containing hair, feathers, or the like

tick in American English 4
a cloth case or covering that is filled with cotton, feathers, hair, etc. to form a mattress or pillow
noun: a score or account

tick in British English 1
noun: a recurrent metallic tapping or clicking sound, such as that made by a clock or watch
verb: to produce a recurrent tapping sound or indicate by such a sound

tick in British English 2
noun: any of various small parasitic arachnids of the families Ixodidae (hard ticks) and Argasidae (soft ticks), typically living on the skin of warm-blooded animals and feeding on the blood and tissues of their hosts: order Acarina (mites and ticks)

tick in British English 3
noun: account or credit (esp in the phrase on tick)

tick in British English 4
noun: the strong covering of a pillow, mattress, etc