Mourning Dress, Mourning Clothes
noun
Your mourning clothes is your mourning dress or mourning clothes.
もふく
The reading comes from the on'yomi for 服 and the kun'yomi for 喪, which you learned with the word 喪. You should know how to read this word!
私の妹は拒食症なのですが、喪服を着ているとより一層痩せ細ってみえました。
My sister is anorexic and when wearing her mourning dress, she looked even skinnier.