Meaning of AM in English

AM

I. a.m. BrE AmE ( also am British English ) /ˌeɪ ˈem/

[ Date: 1700-1800 ; Language: Latin ; Origin: ante meridiem 'before noon' ]

(ante meridiem) used to talk about times that are after ↑ midnight but before ↑ midday ⇨ p.m. :

Work starts at 9 am.

II. am /m, əm; strong æm/ BrE AmE verb

[ Language: Old English ; Origin: eom ]

the first person singular of the present tense of the verb ↑ be

Longman Dictionary of Contemporary English.      Longman - Словарь современного английского языка.