The first word of the phrase is the Tetragrammaton יהוה, the sacred name that, according to the Hebrew Bible, God revealed to the Jews as a chosen people. It is generally translated in English bibles as "the LORD". Jehovah is a Christian anglicized vocalization of this name.
The Septuagint translators believed nis·si′ to be derived from nus (flee for refuge) and rendered it "the Lord My Refuge", while in the Vulgate it was thought to be derived from na·sas′ (hoist; lift up) and was rendered "Jehovah Is My Exaltation".
Matthew Henry considered that Jehovah-nissi–The Lord is my banner "probably refers to the lifting up of the rod of God as a banner in this action. The presence and power of Jehovah were the banner under which they enlisted, by which they were animated and kept together, and therefore which they erected in the day of their triumph."