From sun and tereo; to keep closely together, i.e. (by implication) to conserve (from ruin); mentally, to remember (and obey) -- keep, observe, preserve.
see GREEK sun
see GREEK tereo
a. to preserve (a thing from perishing or being lost): τί, passive (opposed to ἀπολλυσθαι), Matthew 9:17; Luke 5:38 (T WH omit; Tr brackets the clause); τινα, to guard one, keep him safe, from a plot, Mark 6:20 (ἑαυτόν ἀναμάρτητον, 2 Macc. 12:42 (cf. Tobit 1:11; Sir. 13:12)).
b. to keep within oneself, keep in mind (a thing, lest it be forgotten (cf. σύν, II. 4)): πάντα τά ῤήματα, Luke 2:19 (τό ῤῆμα ἐν τῇ καρδία μου, Daniel 7:28, Theod.; τήν γνώμην παῥ ἑαυτό, Polybius 31, 6, 5; (absolutely, Sir. 39:2)).