punctual

from The American Heritage® Dictionary of the English Language, 5th Edition.

• adjective Acting or arriving exactly at the time appointed; prompt.
• adjective Paid or accomplished at or by the appointed time.
• adjective Precise; exact.
• adjective Confined to or having the nature of a point in space.
• adjective Linguistics Of, related to, or being the verbal aspect that expresses momentary action or action considered as having no temporal duration.

from The Century Dictionary.

• Consisting of a point; being a point.
• Exact; precise; nice.
• Exact or prompt in action or in the observance of time, the keeping of appointments, engagements, etc.
• Prompt; at the exact or stipulated time: as, punctual payment.

from the GNU version of the Collaborative International Dictionary of English.

• adjective rare Consisting in a point; limited to a point; unextended.
• adjective Observant of nice points; punctilious; precise.
• adjective Appearing or done at, or adhering exactly to, a regular or an appointed time; precise; prompt.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• adjective prompt or on time
• adjective mathematics Existing as a point or series of points
• adjective linguistics Expressing momentary action that has no duration

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• adjective acting or arriving or performed exactly at the time appointed