The Adamantite Drill is a Hardmodedrill, and is the drill alternative to the Adamantite Pickaxe. Appearances and sounds aside, the two tools are nearly functionally identical. The drill, however is half a second faster. But, unlike pickaxes, most drills cannot be reforged with size, speed, or knockbackmodifiers.
Early into Hardmode, it is usually preferable to save Adamantite for armor and weapons, as the Adamantite Drill does not allow mining any new blocks that the Mythril and Orichalcum pickaxes and drills would not mine.