box vs casket

box and casket both are nouns.

Word	Noun	Adjective	Verb	Adverb
box	Yes	No	Yes	No
casket	Yes	No	Yes	No

As nouns, casket is a hyponym of box; that is, casket is a word with a more specific, narrower meaning than box:

box (noun)	casket (noun)
a blow with the hand (usually on the ear)	small and often ornate box for holding jewels or other valuables
a (usually rectangular) container; may have a lid	box in which a corpse is buried or cremated
separate partitioned area in a public place for a few people
private area in a theater or grandstand where a small group can watch the performance
the driver's seat on a coach
any one of several designated areas on a ball field where the batter or catcher or coaches are positioned
evergreen shrubs or small trees
the quantity contained in a box
a rectangular drawing
a predicament from which a skillful or graceful escape is impossible