1) Matter 2) Pyrectic 3) Substance 
Any substance that produces fever.
• (n.) Electricity. • (n.) A poison separable from decomposed meat infusions, and supposed to be formed from albuminous matter through the agency of bacteria.
(from the article `human disease`) ...large amounts of tissue have died because of lack of blood supply. Body temperature is controlled by the thermostatic centre in the hypothalamus. ... ...fever appears to be a defensive reaction by the body against infectious disease. When bacteria or viruses invade the body and cause tissue injury, ...
<cell biology> Substance or agent that produces fever. The major endogenous pyrogen in mammals is probably interleukin-1. ... (18 Nov 1997) ... 
(pi´ro-jәn) a substance that causes fever. endogenous pyrogen a low-molecular-weight protein that is produced by phagocytic leukocytes in response to stimulation by exogenous pyrogens; it is then released into the circulation, and it induces fever by acting on the preoptic area of t...
Substance or agent that produces fever. The major endogenous pyrogen in mammals is probably interleukin-1.
Pyr'o·gen noun [ See Pyrogenous .] 1. Electricity. [ R.] 2. (Physiol. Chem.) A poison separable from decomposed meat infusions, and supposed to be formed from albuminous matter through the agency of bacteria. 
Type: Term Pronunciation: pī′rō-jen Definitions: 1. A fever-inducing agent; pyrogens are produced by bacteria, molds, viruses, and yeasts.
(pi;ruo-jen) A fever-producing substance.
[n] - any substance that can cause a rise in body temperature
any substance that causes a fever 
pyrectic noun any substance that can cause a rise in body temperature
a substance, as a thermostable bacterial toxin, that produces a rise in temperature in a human or animal.