1. Fair, proper, or moderate under the circumstances ( reasonable pay).
2. According to reason (your argument is reasonable but not convincing).
“It is extremely difficult to state what lawyers mean when they speak of ‘reasonableness.’ In part the expression refers to ordinary ideas of natural law or natural justice, in part to logical thought, working upon the basis of the rules of law.” John Salmond, Jurisprudence 183 n. (u) (Glanville L. Williams ed., 10th ed. 1947).
“In one sense the word [reasonable] describes the proper use of the reasoning power, and in another it is no more than a word of assessment. Reasoning does not help much in fixing a reasonable or fair price or a reasonable or moderate length of time, or in estimating the size of a doubt. Lawyers say a reasonable doubt, meaning a substantial one; the Court of Appeal has frowned upon the description of a reasonable doubt as one for which reasons could be given.” Patrick Devlin, The Judge 134 (1979).
3. (Of a person) having the faculty of reason (a reasonable person would have looked both ways before crossing the street).
4. Archaic. Human (criminal homicide is traditionally called the unlawful killing of a “reasonable person”). — reasonableness, n.
