asymptote
/ˈeɪ̯sɪmtoʊ̯t/noun
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A straight line which a curve approaches arbitrarily closely, as they go to infinity. The limit of the curve, its tangent "at infinity".
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(by extension) Anything which comes near to but never meets something else.
verb
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To approach, but never quite touch, a straight line, as something goes to infinity.