Rationality was the state of being or acting according to logic.
In 2267, Spock said to Montgomery Scott and the crew, "Neither you nor I can be spared here. Mister DeSalle, equip the landing party with full communications, armament, and life-support gear. Mister Jaeger, your geophysical knowledge may be crucial down there. Doctor McCoy will accompany. If those peculiar signals are coming from Captain Kirk or Lieutenant Sulu, their rationality is in question." (TOS: "The Squire of Gothos")