To conceive means to form an idea or plan in your mind, to imagine or think of something for the first time. When an inventor conceives a new machine, they're creating the first spark of the idea before they draw blueprints or build anything. When you conceive a strategy for winning a chess game, you're developing a mental plan for how the pieces should move.

The word suggests the beginning of something: the moment when a thought takes shape in your imagination. Before the Wright brothers built their airplane, they first had to conceive that human flight was even possible. Before you write a story, you conceive the plot and characters in your mind.

Conceive can also mean to understand or grasp an idea, especially something difficult to imagine. You might say, “I can't conceive of a number as large as a trillion,” meaning your mind struggles to truly comprehend it. When someone says an idea is “inconceivable,” they mean it seems impossible to imagine or believe.