Frock and Underclothes

Frock noun - A garment with a joined blouse and skirt usually worn by a woman or girl.

Underclothes and frock are semantically related In some cases you can use "Underclothes" instead a noun "Frock".

Underclothes noun - Clothing intended to be worn underneath other clothing.

Frock and underclothes are semantically related in attire topic. Sometimes you can use "Frock" instead a noun "Underclothes", if it concerns topics such as personal attire.