[or.gan] n [ME, partly fr. OE organa, fr. L organum, fr. Gk organon, lit., tool, instrument; partly fr. OF organe, fr. L organum; akin to Gk ergon work--more at work] (bef. 12c) 1 a archaic: any of various musical instruments; esp: wind instrument b (1): a wind instrument consisting of sets of pipes made to sound by compressed air and controlled by keyboards and producing a variety of musical effects--called also pipe organ (2): reed organ (3): an instrument in which the sound and resources of the pipe organ are approximated by means of electronic devices (4): any of various similar cruder instruments
2. a: a differentiated structure (as a heart, kidney, leaf, or stem) consisting of cells and tissues and performing some specific function in an organism b: bodily parts performing a function or cooperating in an activity "the eyes and related structures that make up the visual ~s"
3: a subordinate group or organization that performs specialized functions "the various ~s of government"
4: periodical