From en and histemi; to place on hand, i.e. (reflexively) impend, (participle) be instant -- come, be at hand, present.
see GREEK en
see GREEK histemi
STRONGS NT 1764: ἐνίστημιἐνίστημι: perfect ἐνέστηκα, participle ἐνεστηκώς (Hebrews 9:9), and by syncope ἐνεστως; future middle ἐνστήσομαι; to place in or among; to put in; in perfect, pluperfect, 2 aorist, and in middle (properly, as it were to stand in sight, stand near) to be upon, impend, threaten: 2 Thessalonians 2:2; future middle 2 Timothy 3:1. perfect participle close at hand, 1 Corinthians 7:26; as often in Greek writings (in the grammarians ὁ ἐνεστως namely, χρόνος is the present tense (cf. Philo de plant. Noë § 27 τριμερης χρόνος, ὅς εἰς τόν παρεληλυθότα καί ἐνεστῶτα καί μέλλοντα τέμνεσθαι πέφυκεν)), present: ὁ καιρός ὁ ἐνεστως, Hebrews 9:9; τά ἐνεστῶτα opposed to τά μέλλοντα, Romans 8:38; 1 Corinthians 3:22; ὁ ἐνεστως αἰών πονηρός in tacit contrast with τῷ μέλλοντι αἰῶνι, Galatians 1:4 (Basil., epistle 57 ad Melet (iii., p. 151 c., Benedict. edition) ὠφέλιμα διδαγματα ἤ ἐφοδια πρός τέ τόν ἐνεστῶτα αἰῶνα καί τόν μέλλοντα). (Many (so R. V.) would adopt the meaning present in 2 Thessalonians 2:2 and 1 Corinthians 7:26 also; but cf. Meyer on Galatians, the passage cited.)