Insensible means unconscious or unaware. When a boxer gets knocked out and lies insensible on the mat, he's completely unconscious and doesn't know what's happening around him. A person who faints becomes temporarily insensible to the world.

The word can also describe being unaware of something in a less dramatic way. Someone might be insensible to the cold, barely noticing freezing temperatures that make everyone else shiver. A person insensible to criticism doesn't seem to notice or care when others point out their mistakes.

In older literature, you might see insensible used to mean lacking feeling or emotion, like when a character is described as insensible to another person's suffering. This suggests not just failing to notice, but showing no emotional response.

Insensible is quite different from insensitive, which means not showing enough consideration for others' feelings. You can be insensible without being insensitive, and vice versa.