The Collaborative International Dictionary of English v.0.48:

Espial \Es*pi"al\, n. [OE. & Norm. F. espiaille. See Espy.]
   1. The act of espying; notice; discovery.
      [1913 Webster]

            Screened from espial by the jutting cape. --Byron.
      [1913 Webster]

   2. One who espies; a spy; a scout. [Obs.] "Their espials . .
      . brought word." --Holland.
      [1913 Webster]

WordNet (r) 3.0 (2006):

espial
    n 1: the act of detecting something; catching sight of something
         [syn: detection, catching, espial, spying,
         spotting]

Moby Thesaurus II by Grady Ward, 1.0:

63 Moby Thesaurus words for "espial":
   bringing to light, bugging, casual discovery, catching,
   chance discovery, cloak-and-dagger work, counterespionage,
   counterintelligence, detection, determination, determining,
   disclosure, discovery, distinguishment, electronic surveillance,
   espionage, excavation, exhumation, exposure, find, finding,
   finding out, following, intelligence, intelligence work, invention,
   locating, location, looking, lookout, lucky strike,
   military intelligence, note, notice, observance, observation,
   recognition, rediscovery, regard, respect, revelation,
   secret police, secret service, serendipity, shadowing, spotting,
   spying, stakeout, strike, surveillance, tailing, trailing,
   treasure trove, trouvaille, trove, uncovering, unearthing, viewing,
   watch, watching, wiretap, wiretapping, witnessing