register vs inventory

register and inventory both are nouns.

Word	Noun	Adjective	Verb	Adverb
register	Yes	No	Yes	No
inventory	Yes	No	Yes	No

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

register: a book in which names and transactions are listed
inventory: (accounting) the value of a firm's current assets including raw materials and work in progress and finished goods

Other hyponyms of register include accounting, accounting system, method of accounting, payroll, paysheet.

register (noun)	inventory (noun)
a regulator (as a sliding plate) for regulating the flow of air into a furnace or other heating device	making an itemized list of merchandise or supplies on hand
an air passage (usually in the floor or a wall of a room) for admitting or excluding heated air from the room	the merchandise that a shop has on hand
a cashbox with an adding machine to register transactions; used in shops to add up the bill	a collection of resources
(computer science) memory device that is the part of computer memory that has a specific address and that is used to hold information of a specific kind	a detailed list of all the items in stock
(music) the timbre that is characteristic of a certain range and manner of production of the human voice or of different pipe organ stops or of different musical instruments	(accounting) the value of a firm's current assets including raw materials and work in progress and finished goods
an official written record of names or events or transactions
a book in which names and transactions are listed

register (verb)	inventory (verb)
enter into someone's consciousness	make or include in an itemized record or report
indicate a certain reading; of gauges and instruments
record in a public office or in a court of law
send by registered mail
manipulate the registers of an organ
be aware of
show in one's face
record in writing; enter into a book of names or events or transactions
enroll to vote
have one's name listed as a candidate for several parties