1. c4 - Noun
2. C4 - Proper noun
C4
(Britain) Abbreviation of Channel 4 (“the British television channel”).
c4 (plural c4s)
(US, politics) A 501(c)(4), an organization that conforms to the United States Internal Revenue Code section 501(c)4
Synonym: 501(c)(4)
Hyponym: spooky PAC