Also, the Companion Bible in it's Appendix 162 remarks:
"In the Greek N.T. two words are used for "the cross", on which the Lord was put to death.1. The word stauros; which denotes an upright pale or stake, to which the criminals were nailed for execution. 2. The word xulon, which generally denotes a piece of a dead log of wood, or timber, for fuel or for any other purpose. It is not like dendron, which is used of a living, or green tree, as in Matt.21: 8; Rev.7: 1, 3; 8:7; 9: 4, &c. As this latter word xulon is used for the former stauros it shows us the meaning of each is exactly the same. The verb stauroo means to drive stakes. Our English word "cross" is the translation of the Latin crux; but the Greek stauros no more means a crux than the word "stick" means a "crutch". Homer uses the word stauros of an ordinary pole or stake, or a simple piece of timber.[ftnote, Iliad xxiv.453. Odyssey xiv.11] And this is the meaning and usage of the word throughout the Greek classics.[ftnote, eg.Thucydides iv.90. Xenophon, Anabasis v.2.21] It never means two pieces of timber placed across one another at any angle, but of always one piece alone. Hence the use of the word xulon(No.2 above)in connection with the manner of our Lord's death and rendered "tree" in Acts 5:30; 10:39; 13:29; Gal.3:13, 1 Pet.2:24. This is preserved in our old English name rood or rod. See Encycl.Brit., 11th (Camb)ed., vol.7, p.505d. There is nothing in the Greek of the N.T. even to imply two pieces of timber."
A Critical Lexicon and Concordance to the English and Greek New Testament, p819. E.W.Bullinger states:
"Used here[cross] for the stauros on which Jesus was crucified. Both words[stauros, xylon]disagree with the modern idea of a cross, with which we have become familiarized by pictures. The stauros was simply an upright pale or stake to which the Romans nailed those who were thus said to be crucified. Stauroo[the verb], merely to drive stakes. It never means two pieces of wood joining each other at any angle. Even the Latin word crux means a mere stake."
The Concordant Literal New Testament with the Keyword Concordance states:
"stauros STANDer: cross, an upright stake or pole, without any crosspiece, now, popularly, cross..."
also
"stauroo cause-STAND, crucify, drive a stake into the ground, fasten on a stake, impale, now by popular usage, crucify, though there was no crosspiece."- pp. 63, 64, Greek-English Keyword Concordance, Concordant Publishing Concern, 1983, 3rd printing of 6th edition of 1976.
The book Dual Heritage-The Bible and the British Museum states: It may come as a shock to know that there is no word such as cross in the Greek of the New Testament. The word translated cross is always the Greek word [stauros] meaning a stake or upright pale. The cross was not originally a Christian symbol; it is derived from Egypt and Constantine.
http://http://onlytruegod.org/defense/stauros.htm