Binary Branching Constraint

In morphology, a Binary Branching Constraint is a constraint on concatenative word formation which says that in the process of word formation only two morphemes can be concatenated at the same time.

In syntax, a Binary Branching Constraint is a constraint proposed in Kayne (1984) which rules out syntactic structures in which a phrase contains more than two immediate constituents (i.e. no node in a tree structure may have more than two branches).

Comment
In the first area, the compound a,i,c either has the structure [a] [b [c]], or the structure a] [[b] [c], but not the ternary structure a] [b] [c. Circumfixes are problematic with respect to this constraint.

Link
Utrecht Lexicon of Linguistics