Noun, pl. kinins
1. Any of various structurally related polypeptides, such as bradykinin and kallikrein. They are members of the autacoid family. They act locally to induce vasodilation and contraction of smooth muscle. It is a component of the kinin-kallikrein system. Their precursors are kininogens. (wikipedia.org)
2. Any of various structurally related polypeptides of the autacoid family, such as bradykinin and kallikrein, that act locally to induce vasodilation and contraction of smooth muscle. (wiktionary.org)
3. One of a number of widely differing substances having pronounced and dramatic physiological effects. Some (e.g., kallidin and bradykinin) are polypeptides, formed in blood by proteolysis secondary to some pathological process, that stimulate visceral smooth muscle but relax vascular smooth muscle, thus producing vasodilation; others (e.g., kinetin) are plant growth regulators. (biology-online.org)
4. Any of a group of substances formed in body tissue in response to injury. They are polypeptides and cause vasodilation and smooth muscle contraction. (Google Dictionary)
Note: In botany, plant hormones cytokinins were first called kinins, but the name was changed to avoid confusion. (wikipedia.org)