From sun and eido; to see completely; used (like its primary) only in two past tenses, respectively meaning to understand or become aware, and to be conscious or (clandestinely) informed of -- consider, know, be privy, be ware of.
see GREEK sun
see GREEK eido
1. to see (have seen) together with others.
2. to see (have seen) in one's mind, with oneself (cf. Fritzsche, Commentary on Romans, vol. i., p. 120; on Mark, pp. 36 and 78; (see σύν, II. 1 and 4)), i. e. to understand, perceive, comprehend: συνιδών, when he had understood it, Acts 12:12 (A. V. considered); Acts 14:6 (became aware) (2 Macc. 4:41 2Macc. 14:26, 30; 3Macc. 5:50; Polybius 1,4, 6; 3, 8, 9; etc.; Josephus, Antiquities 7, 15, 1; b. j. 4, 5,4; Plutarch, Themistius, 7). Perfect σύνοιδα (cf. σύν, as above)
1. to know with another, be privy to (so A. V.): Acts 5:2.
2. to know in one's mind or with oneself; to be conscious of: τί ἐμαυτῷ, 1 Corinthians 4:4 (R. V. know nothing against myself (cf. Wright, Bible Word-Book, 2nd edition, under the word 'By')) (τήν ἀδικίαν, Josephus, Antiquities 1, 1, 4; examples from Greek writings are given by Passow, under the word σύνοιδα, a.; (Liddell and Scott, under the word σύνοιδα, 2); followed by ὅτι (Dionysius Halicarnassus 2:995, 9); the Epistle of Barnabas 1 (4) 3).