Sympathetic awareness of another's suffering joined to a desire to relieve it.
Sympathetic awareness of another's suffering joined to a desire to relieve it — literally “a suffering with.”
The action-oriented member: it adds to the shared or felt awareness of another's distress an urgent desire to help (“pity coupled with an urgent desire to aid or to spare”). On the standard ladder — pity < commiseration < sympathy < compassion — it is the warmest and most morally weighted, and unlike empathy it need not mean absorbing the other's feelings, only valuing their concern enough to act.
Mid-14c., literally “a suffering with another,” from Latin compati “to feel pity” (com- “with” + pati “to suffer”). Latin compassio is a calque of Greek sympatheia.
In use since the 14th century, once able to mean a literal sharing of another's affliction; the core sense (sorrow at another's suffering plus a desire to relieve it) has been stable. (The compound “compassion fatigue” is a modern coinage but doesn't change the base word.) No reliable recent-generation shift.