/fawr'mi kay"sheuhn/ , n.
a tactile hallucination involving the belief that something is crawling on the body or under the skin.
[ 1700-10; formication-, s. of formicatio a sensation that ants are crawling on one's skin, equiv. to formica ( re ) to have such a sensation (v. deriv. of formica ant) + -tion- -TION ]