A person or tool that grubs; something used for digging up roots and stumps from the ground, or a person who works hard for money.
From 'grub' plus the agent suffix '-er' (from Old English), meaning one who does the action or a tool that performs the action.
A grubber is an actual agricultural tool—it looks like a pickaxe and was (and still is) used to remove tree stumps and roots from newly cleared land, backbreaking work.
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