(1):

(n.) One of the principal means of securing unity and consistency in polyphonic composition; the repetition of essentially the same melodic theme, phrase, or motive, on different degrees of pitch, by one or more of the other parts of voises. Cf. Canon.

(2):

(n.) That which is made or produced as a copy; that which is made to resemble something else, whether for laudable or for fraudulent purposes; likeness; resemblance.

(3):

(n.) The act of imitating.

(4):

(n.) The act of condition of imitating another species of animal, or a plant, or unanimate object. See Imitate, v. t., 3.