Definition of "Contraction" :

noun: the act of decreasing (something) in size or volume or quantity or scope

noun: (physiology) a shortening or tensing of a part or organ (especially of a muscle or muscle fiber)

noun: a word formed from two or more words by omitting or combining some sounds

"Won't' is a contraction of will not'."

noun: the process or result of becoming smaller or pressed together

"The contraction of a gas on cooling."