1) Characterized by ludicrous or repulsive distortion; ugly or outlandish in appearance.
2) A decorative painting style invented in ancient Rome–and rediscovered in Renaissance Europe–in which foliage and imaginary figures are combined in fanciful, extravagant designs.
Left: Grotesque fresco decoration in the ceiling of Nero’s Golden House, Rome. 64-68 CE. Right: Nicoletto da Modena. Design for a Panel of Grotesque Ornament. Engraving on paper. Second quarter of the 16th century. Victoria and Albert Museum, London.