nerve

(noun) any bundle of nerve fibers running to various organs and tissues of the body. Synonyms: nervus.

(noun) the courage to carry on. Synonyms: heart, mettle, spunk. Examples: "He kept fighting on pure spunk." "You haven't got the heart for baseball."

(noun) impudent aggressiveness. Synonyms: boldness, brass, face, cheek. Examples: "I couldn't believe her boldness." "He had the effrontery to question my honesty."

(verb) get ready for something difficult or unpleasant. Synonyms: steel.