costume, custom

Costume or costume means an outfit worn to pretend to be someone or something else--
You won't recognize him in his Halloween costume.
We couldn't find a pirate costume, so we'll have to make one.
Costume is also an old-fashioned term for any outfit of clothes--
She looked quaint in her old-fashioned costume.

Custom or custom means a traditional or usual way of doing things--
Bobbing for apples is an old custom.
The local custom is to leave the lights on for the trick-or-treaters.
Custom also means trade or patronage--
If this store doesn't have what I want, I will take my custom elsewhere.
Custom also means made-to-order or made-to-measure--
He had a suit custom-made, and looked very sophisticated.
We will have to order some custom-made drapes, because nothing in the stores is the right size.

 Now that you know that, you can say--
"In America, it is a Halloween custom to wear a costume and go trick-or-treating."

Note--"accustom" ( one word ) means to be used to, or familiar with--
The teacher gave short assignments often, to help accustom the students to regular homework.
Not to be confused with "a custom" ( two words ), meaning a traditional or usual way of doing things--
Our neighbors have a custom of sitting outside on Halloween night.
Note # 2--a "customer" means someone who patronizes a store or business--
"The customer is always right."
Not to be confused with a "costumer", who makes costumes, for the stage, the movies, or for a special event--
The costumer said that our gowns would be ready by the weekend.