Provençal dish of mixed vegetables simmered in olive oil, 1877, from French ratatouille (19c.). The first element is of uncertain etymology, the second is evidently touiller "to stir up," which Ayto writes was "applied, often disparagingly, to any stew," and which Gamillscheg writes is ultimately from Latin tudes "hammer."
late 14c., racional, "pertaining to or springing from reason;" mid-15c., of persons, "endowed with reason, having the power of reasoning," from Old French racionel and directly from Latin rationalis "of or belonging to reason, reasonable," from ratio (genitive rationis) "reckoning, calculation, reason" (see ratio).
In arithmetic, "expressible in finite terms," 1560s. Meaning "conformable to the precepts of practical reason" is from 1630s. Related: Rationally. It is from the same source as ratio and ration; the sense in rational is aligned with that in related reason (n.), which got deformed in French.
"to reason, from two judgments to infer a third," 1640s, from Latin ratiocinatus, past participle of ratiocinari "to reckon, compute, calculate; to deliberate, meditate; to reason, argue, infer" (see ratiocination). "Now rare in serious use" [OED]. Related: Ratiocinant; ratiocinative; ratiocinatory.
1852, "move by means of a ratchet," from ratchet (n.). Transferred sense "cause something (immaterial) to move (up or down) in jerky increments, as if by ratchet" is attested by 1977. Related: Ratcheted; ratcheting.
1620s, "one who follows reason and not authority in thought or speculation," especially "physician whose treatment is based on reasoning," from rational + -ist. In theology/philosophy, "one who applies rational criticism to the claims of supernatural authority or revelation," 1640s. This sense shades into that of "one who believes that human reason, properly employed, renders religion superfluous." Related: Rationalistic; rationalism (1800 in medicine; 1827 in theology, "adherence to the supremacy of reason in matters of belief or conduct;" by 1876 in general use).