Costume - custom

Although these words are translated (into some European languages at least) by the same word (because they have the same root), their meanings in English have diverged. Both are normally nouns.

• Costume is only used for things you wear. Usually, nowadays, it has a sense of an overall 'outfit' or assemblage of garments, often associated with a given ethnicity or nationality or a way of life. This usage can be seen clearly in the US phrase "a costume party", to mean what in Britain is more usually a "fancy-dress party" - an occasion where everyone comes dressed up, let us say as a cowboy, or a pirate, or a member of the crew of the Starship Enterprise. Children love these.

In so far as there is an adjective, it is the noun used epithetically, as in the example above of a "costume party", or a participial adjective from the (unusual) verb 'to costume' - costumed.

• Custom on the other hand means, roughly, 'usual patterns of behaviour'. It can be a count or a non-count noun. We can say "It is my custom to drink coffee at 11:00"; or "The custom at Graduation Day is for the University to begin with the presentation of honorary degrees"; and we can talk of "the customs of the country".

The adjective to describe custom(s) is customary. The associated verb is 'to accustom'. (This can often be heard in a clichéd use of a negative form of the past participle: a modest speaker may start "Unaccustomed as I am to public speaking ... ")

Two particular meanings of custom are connected with the law. In some parts of English law, "custom and practice" can be mentioned as legitimate reasons for certain habits or patterns of behaviour to have started. In the days before wireless, for example, the "custom of the sea" was a common reason for captains of ships to explain their disciplinary actions on board.

And most modern travellers know about the Customs - in the UK, Her Majesty's Customs. These are the body whose job it is to collect taxes on imports and exports, and so on.

An odd quirk of language is that a word of similar meaning to costume and custom - "habit" - has a similar divergence. Habit(s) are customs, patterns of behaviour. A 'habit' is perhaps more fixed, more repetitive than a custom, as we can see from its use to describe addiction: "He was stealing £50 a day to feed his cocaine habit." But upper-class women used to change into riding habits, or specially designed dresses, in order to go on horseback. AWE is tempted to suppose that the two divergences coincide because the garments are thought of as being something worn by custom.