(US, taxation, organizations) An organization that complies with section 501(c)(4) of the U.S. federal tax code. A non-profit organization exempt from some federal income taxes, due to being dedicated social welfare purposes.

Alternative form of 4D chess

(organic chemistry) MPP+, the active metabolite of MPTP.

Under the Whyte notation system, a Mallet-type locomotive with two leading wheels on a leading truck, two sets of six driving wheels, and four trailing wheels on a trailing truck.

Under the Whyte notation system, a Mallet-type locomotive with four leading wheels on a leading truck, two sets of six driving wheels, and two trailing wheels on a trailing truck.

Under the Whyte notation system, a Mallet-type locomotive with two leading wheels on a leading truck, two sets of eight driving wheels, and four trailing wheels on a trailing truck.

Under the Whyte notation system, a Mallet-type locomotive with four leading wheels on a leading truck, two sets of eight driving wheels, and two trailing wheels on a trailing truck.

A tool used in machining fields, especially milling, to aid in setup. It is a block of steel that is precisely squared and parallel whose sides are 2, 4, and 6 inches long, respectively. 2-4-6 blocks are a larger version of the more common 1-2-3 block.

plural of 4-6-6-4

plural of 4-8-8-2