No. You need a dictionary.
Dresses are a specific type of clothing worn by girls/women.
dress (PIECE OF CLOTHING) Show phonetics
noun 
a piece of clothing for women or girls which covers the top half of the body and hangs down over the legs:
a long/short dress
a wedding dress
Costumes are not ordinary clothes. They involve 'dressing up' as something - for example on Halloween the children might wear costumes that make them look like witches, wizards, pumpkins, Elvis, whatever.
1 [C or U] the set of clothes typical of a particular country or period of history, or suitable for a particular activity:
Singers performing Mozart's operas often dress in/wear historical costume.
The dancers leading the procession were in colourful and elaborate costumes.
UK The shop has a good selection of bikinis and bathing/swimming costumes.
2 (UK ALSO fancy-dress costume) a set of clothes worn in order to look like someone or something else, especially for a party or as part of an entertainment:
Our host was wearing a clown costume.
The children were dressed in halloween costumes.