The Collaborative International Dictionary
open-chain
open-chain \open-chain\ adj. (Chemistry) not cyclic; having no rings of atoms within the molecular structure; having an open chain structure. Opposite of cyclic. [Narrower terms: {aliphatic ]
Syn: acyclic.
Wiktionary
open-chain
a. (context organic chemistry English) Having carbon atoms arranged in a linear rather than cyclical chain.