Quick Definition
a vision, supernatural appearance
Strong's Definition
visuality, i.e. (concretely) an apparition
Derivation: from a presumed derivative of G3700 (ὀπτάνομαι);
KJV Usage: vision
Thayer's Greek Lexicon
ὀπτασία, ὀπτασίας, ἡ (ὀπτάζω);
1. the act of exhibiting oneself to view: ὀπτασιαι κυρίου, 2Co_12:1 (A. V. visions; cf. Meyer at the passage) (ἐν ἡμέραις ὀπτασίας μου, Additions to Esther 4:1 , 44 (13) [Esther 4:384:17f]; (cf. Mal_3:2); ἥλιος ἐν ὀπτασία, coming into view, Sir_43:2).
2. a sight, a vision, an appearance presented to one whether asleep or awake: οὐρανίῳ ὀπτασία, Act_26:19; ἑωρακέναι ὀπτασίαν, Luk_1:22; with the genitive of apposition ἀγγέλων, Luk_24:23. A later form for ὄψις (cf. Winers Grammar, 24), Anthol. 6, 210, 6; for ξΗψΐΰΖδ, (Theod.) Dan_9:23; Dan_10:1; Dan_10:7 f.
Mounce Concise Greek Dictionary
ὀπτασία optasia 4x
a vision, apparition, Luk_1:22 ; Luk_24:23 ; Act_26:19 ; 2Co_12:1
Abbott-Smith Greek Lexicon
† ὀπτασία , -ας , ἡ
( < ὀπτάζομαι , Num_14:14 * = ὀπτάνομαι ), later form of ὄψις ,
[in LXX : Mal_3:2 ( H7200 ni .), Da TH Dan_9:23 ; Dan_10:1 ; Dan_10:7-8 ; Dan_10:16 ( H4758 , H4759 LXX , ὅραμα , -σις ), Ezr_4:7 , Sir_43:2 ; Sir_43:16 * ;]
1. an appearing, coming into view (Ma, Es, Sir, ll . c .).
2. a vision: Luk_1:22 ; Luk_24:23 , Act_26:19 , 2Co_12:1 (Da, ll . c ., also in MGr .).†
STEPBible — Tyndale Abridged Greek Lexicon
ὀπτασία, -ας, ἡ
(ὀπτάζομαι, Num.14:14* = ὀπτάνομαι), later form of ὄψις, [in LXX: Mal.3:2 (רָאָה ni.), Da TH Dan.9:23 10:1, 7-8 10:16 (מַרְאֶה, מַרְאָה LXX, ὅραμα, -σις), Est.4:7, Sir.43:2, 16 * ;]
__1. an appearing, coming into view (Ma, Es, Sir, ll. with).
__2. a vision: Luk.1:22 24:23, Act.26:19, 2Co.12:1 (Da, ll. with, also in MGr.).†
(AS)