ra·tion·al 
(răshə-nəl)
(răshə-nəl)adj.
1. Having or exercising the ability to reason. See Synonyms at logical.
2. Consistent with or based on reason or good judgment; logical or sensible: rational decisions.
3. Of sound mind; sane: wondered if the eccentric neighbor was not completely rational.
4. Mathematics Capable of being expressed as a quotient of integers.
n.
Mathematics
Mathematics
A rational number.
[Middle English racional, from Old French racionel, from Latin ratiōnālis, from ratiō, ratiōn-, reason; see REASON.]
ration·al·ly adv.
ration·al·ness n.