a habitual or characteristic manner, mode, or way of doing something; distinctive quality or style, as in behavior or speech

He has an annoying mannerism of tapping his fingers while he talks. They copied his literary mannerisms but always lacked his ebullience.

marked or excessive adherence to an unusual or a particular manner, esp. if affected

Natural courtesy is a world apart from snobbish mannerism.

( usually initial capital letter ) a style in the fine arts developed principally in Europe during the 16th century, chiefly characterized by a complex perspectival system, elongation of forms, strained gestures or poses of figures, and intense, often strident color.

noun

affectation , air , characteristic , eccentricity , foible , habit , idiosyncrasy , oddness , pose , pretension , queerness , quirk , singularity , trait , trick , affectedness , pretense , bearing , individuality , peculiarity , tic