An ecchymosis (/ˌɛkɨˈmoʊsɪs/; Ancient Greek: ἐκχύμωσις, from ἐκ "out" and χέω "I pour") (noun) \e-ki-ˈmō-səs\ is a subcutaneous purpura (extravasation of blood) larger than 1 centimeter or a hematoma, commonly called a bruise, though the terms are not interchangeable. Specifically, bruises are caused by trauma whereas ecchymoses, a type of purpura, are not necessarily caused by trauma.
A broader definition of ecchymosis is the escape of blood into the tissues from ruptured blood vessels. The term also applies to the subcutaneous discoloration resulting from seepage of blood within the contused tissue.
First used in English in the 1541 translation of Galen's Terapentyke; via New Latin from Greek ekchymōsis, from ekchymousthai "to extravasate blood", from ex- and chymos "juice"; cf. enchyma, "tissue infused with organic juice"; elaboration from chyme, the formative juice of tissues.
Hematomas can be subdivided by size. By definition, ecchymoses are 1 centimeter in size or larger, and are therefore larger than petechiae ( less than 2 millimeters in diameter) or purpura (2 millimeters to 1 centimeter in diameter). Hematomas also have a more diffuse border than other purpura.