And Saul armed David with his armour, and he put an helmet of brass upon his head; also he armed him with a coat of mail. 1 Samuel 17:38
Habergeon means a short, sleeveless hauberk or coat of mail. The term is used in the KJV as translation of three Hebrew words, to only one of which it properly applies. That is shiryon, which occurs in 2 Chronicles 26:14 and Nehemiah 4:16, where its plural is translated “coats of mail” by RSV. It is the word for the coat of mail worn by Goliath and for that which Saul put on David and David would not wear (1 Samuel 17:5, 38).
A different word, shiryah, occurs in the description of Leviathan (Job 41) where the KJV renders verse 26: “The sword of him that layeth at him cannot hold: the spear, the dart, not the habergeon.” These are offensive weapons, and “habergeon” is out of place.
RSV translates: "Though the sword reaches him, it does not avail; nor the spear, the dart, or the javelin."
The other word is tahara, which occurs in the description of “the robe of the ephod” which Aaron wore (Exodus 28:32; 39:23). The meaning of this term is uncertain; the Hebrew lexicons state that it probably means a linen corselet. In any case, it is clear that the robe of the ephod was to be put on over the head and slipped down into place on the body, and that tahara refers to a garment that had to be put on in the same way.
The KJV renders Exodus 28:32: “And there shall be an hole in the top of it, in the midst thereof: it shall have a binding of woven work round about the hole of it, as it were the hole of an habergeon, that it be not rent.”
RSV reads: “It shall have in it an opening for the head, with a woven binding around the opening, like the opening in a garment, that it may not be torn.”
In the description of the locusts from the bottomless pit (Revelation 9:1-11) Tyndale and the other sixteenth-century translations said that “they had habbergions, as it were habbergions of yron” (vs. 9). The KJV moved in the right direction by changing “habbergions” to “breastplates.”
But the Greek word thorax, which is here used twice, separated the the Greek word for “like,” meant not only breastplate but the part of the body which the breastplate covers. RSV translates: “they had scales like iron breastplates.” The entire description should be read in both version. In verses 2, 3, 5, 7c, 8, and 9 the same simple Greek word hos occurs, and means “like.” The KJV uses “as” except in 9a, where it uses “as it were.”
(The Bible Word Book, Bridges & Weigle pg 160)