ladies' slipper vs lady slipper

ladies' slipper and lady slipper both are nouns.

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

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

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

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

ladies' slipper (noun)	lady 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