Meaning of “register” - Learner’s Dictionary

register

noun uk us /ˈredʒɪstər/
OFFICIAL LIST [ C ]

an official list of names:

a register of approved builders
the electoral register
LANGUAGE STYLE [ C, U ]

the style of language, grammar, and words used in particular situations:

a formal/informal register
→ See also cash register

(Definition of “register noun” from the Cambridge Learner’s Dictionary © Cambridge University Press)