A third (one third) generally denotes a large portion. And when used in certain passages like Zechariah 13:9 it may also represent a remnant. In Ezekiel 5:12 it is used in both manners - a third is killed by pestilence (large portion), a third by the sword (large portion), and third scattered (a remnant). So it depends where it is applied. In the New Testament (also a Hebrew set of books) we find in the book of Revelation 8:7,9,11,&12 that when it (the number 1/3) applies to destruction it denote a large portion.I hope this helps.
