car seat vs death seat

car seat and death seat both are nouns.

Word	Noun	Adjective	Verb	Adverb
car seat	Yes	No	No	No
death seat	Yes	No	No	No

As nouns, death seat is a hyponym of car seat; that is, death seat is a word with a more specific, narrower meaning than car seat:

car seat: a seat in a car
death seat: the car seat beside the driver of an automobile; believed to be the most dangerous place to sit in a car in case of an accident

car seat (noun)	death seat (noun)
a seat in a car	the car seat beside the driver of an automobile; believed to be the most dangerous place to sit in a car in case of an accident