(1) Open to some influence; responsive. (2) Able to be submitted to an action or process.
Impressed with her intelligence and self-confidence, he was highly susceptible to her influence.
With its prefix sus-, "up," susceptible refers to what "takes up" or absorbs like a sponge. When negotiating the settlement of World War II at Yalta with Churchill and Roosevelt, Stalin may have found the other two susceptible to his threats and bullying and thus managed to hold on to much of Eastern Europe. Students are usually susceptible to the teaching of a strong and imaginative professor. In a similar way, a sickly child will be susceptible to colds, and an unlucky adult will be susceptible to back problems.