tic / tick are similar-sounding terms with different meanings (referred to as homophones). To better understand the differences, see below for definitions, pronunciation guides, and example sentences using each term. 👇
tic: (noun) a local and habitual twitching especially in the face.
tick: (noun) a metallic tapping sound. (noun) any of two families of small parasitic arachnids with barbed proboscis; feed on blood of warm-blooded animals. (noun) a light mattress. (verb) make a sound like a clock or a timer. (verb) sew.
tic: t·IH·k
tick: t·IH·k
(Examples are Wikipedia snippets under the CC ShareAlike 3.0 license. Definitions drawn from WordNet.)