Momentary sighting (7)
I believe the answer is:
glimpse
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">momentary sighting</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for glimpse that I've seen before include "Notice" , "Glance, catch sight of" , "Momentary sighting" , "spot" , "Just a fleeting sighting" .)