arms and weaponry taken collectively: the equipment of war, and by extension the armory that stores it or the battle waged with it
Nesheq is a collective word: it names weaponry as a whole, the arms and gear of war gathered under one term, rather than a single sword or bow. When a king's tribute includes nesheq, or an army burns the enemy's nesheq, the picture is a whole stockpile of military equipment.
From that core the word stretches in two natural directions. Because a store of weapons implies the room that holds it, nesheq can name the armory itself, as at the ascent to the arsenal in Jerusalem's wall (Nehemiah 3:19). And because weapons are what a battle is fought with, the phrase "the day of nesheq" means simply the day of battle (Psalm 140:7).
Hebrew has a broader word for war-gear, כְּלִי, which means any implement or vessel and only carries the sense "weapon" inside the phrase "weapons of war"; nesheq, by contrast, is arms as such. The nearest Greek counterpart is ὅπλον, the collective "arms" or "armor" of the New Testament.