(1) Denature, used to describe RNA polymerase action in decoupling DNA base pairs. (2) To make the transition from solid to liquid, a process in which ions or molecules leave ordered position and acquire random motions. (3) to undergo any of several processes in which molecules or parts of molecules acquire greater random movement (e.g., tumbling motion of lipid hydrocarbon chains within a biologic membrane, disruption of base stacking in nucleic acid on heating). (4) A molten substance.