Reasonable (adjective)

1. Fair, just and not excessive.
2. Able to be justified or explained.
3. Based on good judgment or sound thinking.
4. Proportionate to the circumstances or needs.

Origin:

From old french raisonable, from raison "reason".

Examples:

1. The price is reasonable.
2. His request was reasonable.
3. She has a reasonable explanation.
4. The decision was reasonable.
5. The terms of the agreement were reasonable.