MERCU'RIAL, adjective [Latin mercurialis.] 1. Formed under the influence of Mercury; active; sprightly; full of fire or vigor; as a mercurial youth; a mercurial nation. 2. Pertaining to quicksilver; containing quicksilver, or consisting of mercury; as mercurial preparations or medicines.
Source: Webster's 1828 American Dictionary ↗ · public-domain · returned verbatim, no AI