supersaturated vapor
Technical term used in physics and meteorology for vapor that exceeds its equilibrium saturation point without condensing.
Supersaturated vapor is used in cloud chambers to observe radiation tracks.
Saturated vapor; 過飽和蒸気 is vapor that has gone beyond the saturation point, while 飽和蒸気 is at equilibrium.
Compound of 過 (excess) + 飽和 (saturation) + 蒸気 (vapor). A straightforward technical term with no obscure historical derivation.