/ˈôrgən/
Noun, pl. organs
(Biology)
1. A collection of tissues joined in a structural unit to serve a common function. (wikipedia.org)
2. A part of an organism that is typically self-contained and has a specific vital function, such as the heart or liver in humans. (Google Dictionary)
Word origin: The meaning “body part adapted to a certain function” is attested from late 14c., from a Medieval Latin sense of Latin organum.