Concise Bible Dictionary:

The wooden structure to which criminals were nailed. Jesus died on a cross: hence it is an emblem of the crucifixion of Christ, so that we read of the “death of the cross,” and the “blood of his cross” (Phil. 2:88And being found in fashion as a man, he humbled himself, and became obedient unto death, even the death of the cross. (Philippians 2:8); Col. 1:2020And, having made peace through the blood of his cross, by him to reconcile all things unto himself; by him, I say, whether they be things in earth, or things in heaven. (Colossians 1:20)); also the “preaching of the cross” (1 Cor. 1:1818For the preaching of the cross is to them that perish foolishness; but unto us which are saved it is the power of God. (1 Corinthians 1:18)). The cross of Christ makes nothing of man and sets aside all his pretensions: therefore to preach “the cross” arouses man’s hatred and persecution (Gal. 5:1111And I, brethren, if I yet preach circumcision, why do I yet suffer persecution? then is the offence of the cross ceased. (Galatians 5:11); Gal. 6:12,1412As many as desire to make a fair show in the flesh, they constrain you to be circumcised; only lest they should suffer persecution for the cross of Christ. (Galatians 6:12)
14But God forbid that I should glory, save in the cross of our Lord Jesus Christ, by whom the world is crucified unto me, and I unto the world. (Galatians 6:14)
). “The cross” is also a symbol of the shame and self-denial that lie in the believer’s path. He is exhorted to take up his cross daily and follow the Lord (Luke 9:2323And he said to them all, If any man will come after me, let him deny himself, and take up his cross daily, and follow me. (Luke 9:23)).

Strong’s Dictionary of Greek Words:

from the base of 2476; a stake or post (as set upright), i.e. (specially), a pole or cross (as an instrument of capital punishment); figuratively, exposure to death, i.e. self-denial; by implication, the atonement of Christ
KJV Usage:

From Manners and Customs of the Bible:

A cross sufficiently large and strong to hold the body of a man, and long enough to allow a suitable portion to rest in the ground, would be too heavy for any ordinary man to carry. Some have, therefore, supposed that the cross which the condemned bore, according to the Roman law, was merely a miniature representation of the cross on which he was to suffer death; and that he was compelled to carry it to the place of execution to indicate to the spectators in the streets through which he passed the kind of death he was about to suffer. It would thus be a public badge of his shame. Lipsius, however, says that only a part of the cross was borne by the condemned, and that this part was the horizontal beam, which was the lighter of the two pieces of which the cross was composed. The heavier part, the perpendicular, was either planted in the earth before the arrival of the procession, or was ready to be set up as soon as the condemned man arrived with the transverse beam.

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