lady's-slipper vs ladies' slipper

lady's-slipper and ladies' slipper both are nouns.

Word	Noun	Adjective	Verb	Adverb
lady's-slipper	Yes	No	No	No
ladies' slipper	Yes	No	No	No

As nouns, lady's-slipper and ladies' slipper are synonyms defined as:

lady's-slipper and ladies' slipper: any of several chiefly American wildflowers having an inflated pouchlike lip; difficult or impossible to cultivate in the garden

Other synonyms of lady's-slipper include lady's slipper, lady-slipper, lady slipper, slipper orchid.

lady's-slipper (noun)	ladies' slipper (noun)
any of several chiefly American wildflowers having an inflated pouchlike lip; difficult or impossible to cultivate in the garden	any of several chiefly American wildflowers having an inflated pouchlike lip; difficult or impossible to cultivate in the garden