What weapon did Ahimelech the priest give David at Nob?

Answer: Goliath's sword

Goliath's sword was kept at Nob, wrapped in a cloth behind the ephod. David said, "There is none like it; give it to me."

“The priest replied, “The sword of Goliath the Philistine, whom you killed in the Valley of Elah, is here; it is wrapped in a cloth behind the ephod. If you want, you may take it. For there is no other but this one here.” And David said, “There is none like it; give it to me.””— 1 Samuel 21:9 (BSB)