Clothes are garments which consist of 'cloth'es. So it is like there is no singular form of it. But in Turkish, a skirt, a shirt, pants erc. is a 'giysi'. So it can be singular but since its corresponding word in English is only plural they say 'giysi-ler'.
An 'elbise' is a dress. But you can witness some people use it as 'giysi'.
And kıyafet and giysi are interchangable.