TIL !
1. ἄλογος (alogos, Greek for unsayable or unreasonable)
2. irrationalis (Latin translation of ἄλογος)
3. rationalis (Latin backformation)
4. irrational/rational (English translation)
5. ratio (English backformation)
Steps 3 and 5, the backformations, are perhaps in the opposite direction one would expect.
https://english.stackexchange.com/a/218079
reply
TIL !