To surmise means to guess or conclude something based on incomplete information or evidence. When you surmise, you're making an educated guess about what might be true, even though you don't have all the facts yet.

If you walk into your kitchen and see cookie crumbs on the counter, an empty milk glass, and your sister looking guilty, you might surmise that she just ate the last cookie. You didn't actually see her do it, but the clues point in that direction. A detective might surmise that a crime happened at night based on witness statements and other evidence, even without knowing the exact time.

Surmise sits between wild guessing and knowing for certain. It's more thoughtful than a random guess but less confident than a definite conclusion. You use reasoning and observation, but you acknowledge that you might be wrong.

You can also use surmise as a noun: “My surmise is that the package will arrive tomorrow.” This means your best guess, based on what you know about shipping times and tracking information, is that tomorrow is the likely delivery day.