Hello Edson, The most common meaning refers to a complete style of dressing that involves not only the clothes, but also accessories etc...., that are worn one time as in a particular country or period or in particular events( as Mister Wright mentioned) such as a dress ball, festive occasions like a carnival or by an actor in a play.

The most usual use of the word is to describe a certain style of clothing that you wear on a special occasion. It's also clothing used to disguise your self- to hide your identity. At Halloween, people dress up in costumes. The portuguese "costume" is not a cognate, in case you were wondering. The portuguese "costume" is translated as "custom" or habbit" in english.

this are my answer. 1.The attire worn in a play or at a fancy dress ball "he won the prize for best costume" 2.Unusual or period attire not characteristic of or appropriate to the time and place "in spite of the heat he insisted on his woollen costume" 3.The prevalent fashion of dress (including accessories and hair style as well as garments 4.The attire characteristic of a country or a time or a social class "he wore his national costume" cowboy...