毒 'poison' + 辣 'spicy/hot' — literally 'poisonous and spicy', a vivid image for cruelty that burns and harms. Often pairs with 心狠手辣 (xīnhěnshǒulà) 'ruthless and cruel'.
usage
Describes both people/methods (cruel, sinister) and the sun (scorching, harsh). The latter usage is mostly literary or written.
