...I don't think it's a weed.
It looks familiar, but my brain is totally smooth today.
Here is a link that might be useful: thread on weeds forum
It looks familiar to me too. I don't have a plant to compare it to right now, but I think it might be an avacado seed that sprouted. I compost in place and have them come up a lot. Whoever has it growing could dig down and might be able to find the seed.
The leaves look like my loquat tree.