The Hebrew word et (distinct from the common direct-object marker) refers to a plowing tool — a plowshare, mattock, or similar iron implement used in agriculture. It appears in a famous passage in 1 Samuel describing Philistine domination of Israel's metal-working.
The absence of plowshares in 1 Samuel 13 represents Philistine oppression — Israel was disarmed, forbidden from sharpening their own agricultural tools, let alone weapons. The same imagery is reversed in the great eschatological vision of Isaiah and Micah, where nations 'beat their swords into plowshares' (ittim). The plowshare thus symbolizes both the weight of oppression and the promise of peace. In the kingdom of God, instruments of war become instruments of cultivation — creation restored, violence ended, productivity flourishing.