The story
A shortened form of "constituent command." The term may also have been chosen so as to eliminate confusion in speech with the similar notion kommand.
Etymology from Wiktionary, CC BY-SA 4.0.
c-command
Today it means: The relationship between a node in a parse tree and its sibling nodes (usually meaning the children of the first branching node that dominates the node) and all the sibling nodes' children. Full definition →