Noticeable or able to be felt by the senses.
Example:
Her change in attitude toward him was barely perceptible, and he couldn't be sure that he wasn't imagining it.
Perceptible includes the prefix per-, meaning "through," so the word refers to whatever can be taken in through the senses. A perceptive person picks up hints and shades of meaning that others can't perceive. Such people rely on their sharp perceptions, their observations of whatever kind. So very often what is perceptible to one person -- a tiny sound, a slight change in the weather, a different tone of voice -- will not be to another.