From the same as opisthen with enclitic of direction; to the back, i.e. Aback (as adverb or preposition of time or place; or as noun) -- after, back(-ward), (+ get) behind, + follow.

see GREEK opisthen

1. adverbially of place: ἑστάναι, Luke 7:38; ἐπιστρέψαι ὀπίσω, back, Matthew 24:18 (ὑποστρέφειν ὀπίσω, Josephus, Antiquities 6, 1, 3); τά ὀπίσω, the things that are behind, Philippians 3:13 (14); εἰς τά ὀπίσω ἀπέρχεσθαι, to go backward, Vulg.abire retrorsum, John 18:6; to return home, of those who grow recreant to Christ's teaching and cease to follow him, John 6:66; στρέφεσθαι, to turn oneself back, John 20:14; ἐπιστρέφειν, to return back to places left, Mark 13:16; Luke 17:31; ὑποστρέψαι εἰς τά ὀπίσω, tropically, of those who return to the manner of thinking and living already abandoned, 2 Peter 2:21 Lachmann; βλέπειν (Vulg. (aspicere or)respicere retro (A. V. to look back)), Luke 9:62.

2. By a usage unknown to Greek authors, as a preposition with the genitive (Winers Grammar, § 54, 6; Buttmann, § 146, 1);

a. of place: Revelation 1:10 (WH marginal reading ὄπισθεν); (Numbers 25:8; Song of Solomon 2:9); in phrases resembling the Hebrew (cf. Winers Grammar, 30; Buttmann, as above and 172 (150)): ὀπίσω τίνος ἔρχεσθαι to follow anyone as a guide, to be his disciple or follower, Matthew 16:24; Luke 9:23; Mark 8:34 R L Tr marginal reading WH; (cf. Luke 14:27); also ἀκολουθεῖν, Mark 8:34 G T Tr text; Matthew 10:38 (see ἀκολουθέω, 2 at the end); πορεύεσθαι, to join oneself to one as an attendant and follower, Luke 21:8 (Sir. 46:10); to seek something one lusts after, 2 Peter 2:10 (cf. Winers Grammar, 594 (553); Buttmann, 184 (160)); ἀπέρχομαι ὀπίσω τίνος, to go off in order to follow one, to join one's party, Mark 1:20; John 12:19; to run after a thing which one lusts for (cf. Buttmann, as above), ἑτέρας σαρκός, Jude 1:7; δεῦτε ἐπίσω μου (see δεῦτε, 1), Matthew 4:19; Mark 1:17; ἀποστέλλειν τινα ὀπίσω τίνος, Luke 19:14; ἀφισταναι, ἀποσπᾶν, τινα ὀπίσω αὐτοῦ, to draw one away to (join) his party, Acts 5:37; Acts 20:30; ἐκτρέπεσθαι, to turn out of the right path, turn aside from rectitude, 1 Timothy 5:15; by a pregnant construction, after θαυμάζειν, to wonder after i. e. to be drawn away by admiration to follow one (Buttmann, 185 (160f)), Revelation 13:3 (πᾶς ὁ λαός ἐξέστη ὀπίσω αὐτοῦ, 1 Samuel 13:7); ὕπαγε ὀπίσω μου (A. V. get thee behind me), out of my sight: Luke 4:8 R L brackets; Matthew 4:10 (G L brackets); ; Mark 8:33.

b. of time, after: ἐρήξεσθαι ὀπίσω τίνος, to make his public appearance after (subsequently to) one, Matthew 3:11; Mark 1:7; John 1:15, 27, 30 (ὀπίσω τοῦ σαββάτου, Nehemiah 13:19).