means A scientist who studies matter, energy, and the fundamental laws governing how they behave.

from From Greek 'physis,' meaning 'nature' — the same root that gives us 'physics' and even 'physician' (originally just 'one who knows nature'). The word 'physicist' itself is a relatively late English coinage, an early-19th-century invention reportedly proposed to give natural philosophers a name as tidy as their equations.