Vincible describes something that is easily overcome, like a young and inexperienced army or a mild fear of heights.
You're probably more familiar with the antonym of vincible, the adjective invincible, which means "unbeatable." Its opposite is much more rarely used, but it can be useful for talking about something — or someone — that can be defeated. The Latin root word of vincible, vincere, means "to conquer," and it's also the origin of the words victor and victorious.