1) to look at, behold
2) to allow one's self to be seen, to appear
Part of Speech: verb
Citing in TDNT: 5:315, 706
The first a (middle voice) prolonged form of the second (primary) which is used for it in certain tenses; and both as alternates of G3708; to gaze (that is, with wide open eyes, as at something remarkable; and thus differing from G991, which denotes simply voluntary observation; and from G1492, which expresses merely mechanical, passive or casual vision; while G2300, and still more emphatically its intensive G2334, signifies an earnest but more continued inspection; and G4648 a watching from a distance): - appear, look, see, shew self.
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Perseus Digital Library
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From this site's dictionary (in Italian)
Click on the first column to search for that word as a form of the root ὀπτάνομαι; click on the second column to search for that grammatical form of the root ὀπτάνομαι; click on the third column to search for that word and grammatical form; click on the total to search for the root ὀπτάνομαι.