Loom has two distinct meanings. First, a loom is a tool for weaving. Second, to loom is to appear or stand over someone in a threatening way. Don’t loom over the person you’re teaching to weave! You'll just make her nervous.
The word loom, as an instrument to turn yarn into fabric, comes from an Old English word for “tool.” The verb form, meaning “to lurk just out of view,” comes from Low German or Dutch. Anything that looms is coming into view slowly and isn't something you want to see. Although storm clouds and icebergs can loom, this word does not have to refer to a physical object. If a deadline looms, better get to work.