petticoat vs half-slip

petticoat and half-slip both are nouns.

Word	Noun	Adjective	Verb	Adverb
petticoat	Yes	No	No	No
half-slip	Yes	No	No	No

As nouns, petticoat and half-slip are synonyms defined as:

Other synonyms of petticoat include underskirt.

petticoat (noun)	half-slip (noun)
undergarment worn under a skirt	undergarment worn under a skirt