Definition of "coupler" [coup•ler]

• One that couples, especially a device for coupling two railroad cars. (noun)
• A device connecting two organ keyboards so that they may be played together. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "Shortly after the introduction of pneumatic action, an organ with an occasional octave coupler, that is a coupler which depressed a key an octave higher or lower than the one originally struck, was sometimes met with."
• "Mr. Beard invented also a car-coupler which is used on a great many railroads throughout the United States."
• "Yes you can connect that to your mac with the "coupler" you've bought"