From theros (in the sense of the crop); to harvest -- reap.
see GREEK theros
a. properly: Matthew 6:26; Luke 12:24; James 5:4; (figuratively, John 4:36 (twice)).
b. in proverbial expressions about sowing and reaping: ἄλλος ... ὁ θερίζων, one does the work, another gets the reward, John 4:37f (where the meaning is 'ye hereafter, in winning over a far greater number of the Samaritans to the kingdom of God, will enjoy the fruits of the work which I have now commenced among them' (others do not restrict the reference to converted Samaritans)); θερίζων ὅπου οὐκ ἔσπειρας, unjustly appropriating to thyself the fruits of others' labor, Matthew 25:24, 26; Luke 19:21f; ὁ ἐάν ... θερίσει, as a man has acted (on earth) so (hereafter by God) will he be requited, either with reward or penalty (his deeds will determine his doom), Galatians 6:7 (a proverb: ut sententem feceris, ita metes, Cicero, de orat. 2, 65; (σύ δέ ταῦτα αἰσχρῶς μέν ἔσπειρας κακῶς δέ ἐθερισας, Aristotle, rhet. 3, 3, 4; cf. Plato, Phaedr. 260 d.; see Meyer on Galatians, the passage cited)); τί, to receive a thing by way of reward or punishment: τά σαρκικά, 1 Corinthians 9:11; φθοράν, ζωήν αἰώνιον, Galatians 6:8, (σπείρειν πυρούς, θερίζειν ἀκάνθας, Jeremiah 12:13; ὁ σπείρων φαῦλα θερίσει κακά, Proverbs 22:8; ἐάν σπείρητε κακά, πᾶσαν ταραχήν καί θλῖψιν θερισετε, Test. xii. Patr., p. 576 (i. e. test. Levi § 13)); absolutely: of the reward of well-doing, Galatians 6:9; 2 Corinthians 9:6.
c. As the crops are cut down with the sickle, θερίζειν, is figuratively used for to destroy, cut off: Revelation 14:15; with the addition of τήν γῆν, to remove the wicked inhabitants of the earth and deliver them up to destruction, Revelation 14:16 (τήν Ἀσίαν, Plutarch, reg. et. imper. apophthegm. (Antig. 1), p. 182 a.).