As soon as seen, or presented to sight.

(idiomatic) Immediately when sighted. / (by extension) Immediately something has come to one's attention.

(climbing) An ascent of a route without falling, when one has been advised on it or has seen it.

In a place where something can be seen. / Figuratively near or close in either distance or time.

(firearms) To align the sights of a firearm.

(obsolete) Easily or clearly seen; distinctly visible; perspicuous / Having full sight; clear-sighted; perspicacious and discerning; observant

The state of being sightful; perspicuity.

When seeing.

By appearance.

plural of on sight