plenum (n.) Look up plenum at Dictionary.com
1670s, "filled space" (opposite of vacuum), from Latin plenum (spatium) "full (space)," neuter of adjective plenus "full, filled, greatly crowded; stout, pregnant; abundant, abounding; complete," from PIE root *pele- (1) "to fill." The meaning "of a full assembly of legislators" is first recorded 1772.