An Etymological Dictionary of Astronomy and Astrophysics

1. General: Any theorem that expresses various reciprocal relations for the behavior of some physical systems, in which input and output can be interchanged without altering the response of the system to a given excitation.
   

2. In classical electromagnetism, the theorem stating that the current in a detector divided by the voltage at the source remains constant when source and detector are interchanged, as long as the frequency and all the impedances are left unchanged.

Etymology (EN): Reciprocity, from L. reciproc(us) “returning the same way, alternating” + → -ity; → theorem.

Etymology (PE): Farbin, → theorem; dosuyegi, quality noun of dosuyé nuanced term of dosu “two-sided,” from do, → two,

• su “direction, side,” from Mid.Pers. sôk “direction, side.”