lobby (n.)
1530s, "cloister, covered walk," from Medieval Latin laubia, lobia "covered walk in a monastery," from a Germanic source (compare Old High German louba "hall, roof;" see lodge (n.)). Meaning "large entrance hall in a public building" is from 1590s. Political sense of "those who seek to influence legislation" is attested by 1790s in American English, in reference to the custom of influence-seekers gathering in large entrance-halls outside legislative chambers.
lobby (v.)
"seek to influence legislation," 1826, American English, from lobby (n.). Related: Lobbied; lobbying.