From the root of zeugnumi (to join, especially by a "yoke"); a coupling, i.e. (figuratively) servitude (a law or obligation); also (literally) the beam of the balance (as connecting the scales) -- pair of balances, yoke.
1. a yoke;
a. properly, such as is put on draught-cattle.
b. metaphorically, used of any burden or bondage: as that of slavery, 1 Timothy 6:1 (Leviticus 26:13), δουλείας, Galatians 5:1 (Sophocles Aj. 944; δουλοσυνης, Demosthenes 322, 12); of troublesome laws imposed on one, especially of the Mosaic law, Acts 15:10; Galatians 5:1; hence, the name is so transferred to the commands of Christ as to contrast them with the commands of the Pharisees which were a veritable 'yoke'; yet even Christ's commands must be submitted to, though easier to be kept: Matthew 11:29f (less aptly in Clement of Rome, 1 Cor. 16, 17 [ET] Christians are called οἱ ὑπό τόν ζυγόν τῆς χάριτος ἐλθόντες (cf. Harnack at the passage)).
2. a balance, pair of scales: Revelation 6:5 (as in Isaiah 40:12; Leviticus 19:36; Plato, rep. 8, 550 e.; Aelian v. h. 10, 6; others).