(1):

(n.) The result of abbreviating; an abridgment.

(2):

(n.) The form to which a word or phrase is reduced by contraction and omission; a letter or letters, standing for a word or phrase of which they are a part; as, Gen. for Genesis; U.S.A. for United States of America.

(3):

(n.) One dash, or more, through the stem of a note, dividing it respectively into quavers, semiquavers, or demi-semiquavers.

(4):

(n.) The act of shortening, or reducing.