An adjective describes a noun.
vacillating
It is an adjective. To use it as an adverb, you would add -LY (vacantly).
"Ocean water has more salt than fresh water."
To use squeak as an adjective, you would say squeaky.He was a squeaky little mouse.
Stubborn
you use marine to describe a fish
As strong as an ox.
You would have to use the adjective form, which is expeditious. "An expeditious program of renovation allowed the factory to continue its operations."
The adjective is landlocked. Example sentence:Although technically a landlocked state, Michigan is surrounded on three sides by water.
Pure is "Puro/a" and Clean is "Limpio/a" If the object that your are describing is masculine, then you would use the 'o' ending on the adjective. If the object is feminine, then you would use the 'a' ending on the adjective.
The noun slipper does not have an adjective: you would use the noun as a noun adjunct.*The word slippers (slip-on shoes) is not directly related to the adjective slippery.