If you spot something, you descry it. When you spy it, you descry it. It's a good verb to use when you catch a glimpse of a rare bird in the trees. Or when you finally spot Waldo in a "Where's Waldo?" book.
Descry is very similar to "see" or "discern," but involves more than just keeping your eyes open. Usually you descry something after observing carefully for a while. Wrote Ovid, the Ancient Roman poet and author: “Time on time revolving we descry, so moments flit, so moments fly.” Apparently, even in antiquity people complained about seeing the time go by too quickly.