1) Building block 2) Unit 
• (a.) Pertaining to, or formed from, two molecules; as, a bimolecular reaction (a reaction between two molecules).
See molecularity.
Involving two molecules, as in a bimolecular reaction. ... (05 Mar 2000) ... 
Bi'mo·lec'u·lar adjective [ Prefix bi- + molecular .] (Chemistry) Pertaining to, or formed from, two molecules; as, a bimolecular reaction (a reaction between two molecules). 
Type: Term Pronunciation: bī′mō-lek′yū-lăr Definitions: 1. Involving two molecules, as in a bimolecular reaction.
[adj] - relating to or affecting two molecules
adjective relating to or affecting two molecules
having or involving two molecules.