Yes, register is a Scrabble word!

Verb

1. Record in writing; enter into a book of names or events or transactions

2. Record in a public office or in a court of law

3. Enroll to vote

4. Be aware of

5. Indicate a certain reading; of gauges and instruments

6. Have one's name listed as a candidate for several parties

7. Show in one's face

8. Manipulate the registers of an organ

9. Send by registered mail

10. Enter into someone's consciousness

Noun

1. An official written record of names or events or transactions

2. (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

3. A book in which names and transactions are listed

4. (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

5. An air passage (usually in the floor or a wall of a room) for admitting or excluding heated air from the room

6. A regulator (as a sliding plate) for regulating the flow of air into a furnace or other heating device

7. A cashbox with an adding machine to register transactions; used in shops to add up the bill