From Medieval Latin 'lobia' (covered walkway), from Germanic *laubo (leaf) — from leafy arbor to political influence.
A large entrance hall or waiting area in a public building, hotel, or theater; also, a group of people seeking to influence legislators or public officials.
From Medieval Latin 'lobia' or 'laubia' (a covered walkway, a gallery, a cloister), from Frankish *laubja (a shelter, a covered hall), from Proto-Germanic *laubō (a leaf, foliage — hence a leafy shelter, an arbor), from PIE *lewbʰ- (to peel, to strip bark). The semantic progression moves from 'leaf' to 'leafy shelter' to 'covered walkway' to 'entrance hall.' The political sense emerged in the seventeenth century from the lobby of the House
The political sense of 'lobby' — meaning to influence legislators — comes from the specific lobby of the British House of Commons, where members of the public could wait and approach Members of Parliament. The word 'lobbyist' first appeared in American English in the 1840s, derived from this architectural feature of the British Parliament.