Bluish means somewhat blue or having a hint of blue color mixed with another color. When something looks bluish, it's not quite fully blue but has enough blue in it that you notice. A winter sky might look bluish-gray before a snowstorm, or someone's lips might turn bluish from being very cold.

The word helps describe colors that fall between categories. Maybe you're painting and mix blue with white to create a bluish tint, or you notice the bluish glow of your computer screen in a dark room. A bruise often looks bluish-purple as it heals.

Scientists use bluish to describe precise observations: astronomers note the bluish light from certain hot stars, while marine biologists describe the bluish tint of some fish scales. When you can't quite call something “blue” but blue is definitely part of what you're seeing, bluish is the perfect word.