If we take the example of following conversation: A: "I am so hungry, I haven't eaten something for ages." B: "Oh, I am so sorry for your plight!" You see, there is no action followed after the conversation, only words. This means "B" is a sympathetic person. In contrast to this example: A: "I am so hungry, I haven't eaten something for ages." B: "Oh, poor you - here you are some gloceries" In this case you are not only sympathetic but compassionate. It means there is an immediate action following - so in this situation "B" is a compassionate person.

Compassion is generally considered a personality or character trait. Someone who is often sympathetic to others' misfortune is compassionate. Sympathy is sharing someone else's emotions (usually negative emotions) in a given instance. It comes from the prefix "sym-" meaning "same" and the greek root "path" meaning "feeling." Compassion is understanding someone's suffering (but never happiness or anger). It comes from the prefix "com-/con-" meaning "with/together" and "passion," meaning "suffering."

sympathy is when you feel bad for someone - or their situation - like feeling sorry for someone compassion is simply having deep feelings or emotions about something. (the dictionary says a feeling of deep sympathy and sorrow for another who is stricken by misfortune, accompanied by a strong desire to alleviate the suffering).