Among the OED definitions are these obsolete ones:
"One who conducts, negotiates, or transacts matters on behalf of another
or others; a representative, agent, or deputy. Obs.
An official having charge of the King's or Queen's interests. Obs.
One properly qualified and formally admitted to practise as a law-agent
in any court; formerly, one practising in a court of equity, as
distinguished from an attorney.
One who entreats, requests, or petitions; one who solicits or begs
favours; a pleader, intercessor, advocate".
In the USA, you often see official looking signs in public places,
saying "No Solicitors". The definition of Solicitor in the USA is
rather different from the one we use:
U.S. One who solicits business orders, advertising, etc.