1.  rf(n = noun.substance) releasing factor, releasing hormone - a substance produced by the hypothalamus that is capable of accelerating the secretion of a given hormone by the anterior pituitary gland;
is a kind of factor
has particulars: ghrf, growth hormone-releasing factor

2.  rf(n = noun.substance) atomic number 104, element 104, rutherfordium, unnilquadium, unq - a radioactive transuranic element which has been synthesized;
is a kind of chemical element, element

3.  rf(n = noun.body) reticular formation - a complex neural network in the central core of the brainstem; monitors the state of the body and functions in such processes as arousal and sleep and attention and muscle tone;
is a kind of neural net, neural network
is a part of brain-stem, brain stem, brainstem
has parts: ras, reticular activating system

rf, symb. Chem. the element rutherfordium.