At first it sounded like you were describing the common weed known as Burdock that is often mistaken for rhubarb.

But from the description of the yellow flowers, I think you have what is known as Ligularia.

They sell it at Steins for $29.95 in a gallon container.

I bought one and now have it coming up all over my property. I would not call it invasive like BeeBalm or Black-Eyed-Susan but it does pop up in the strangest places. It can easily be dug out and gotten rid of if it appears in a spot where it is not wanted. It it a shade plant and does not do well in sunny lawns so not to worry about that happening.

Ligularia grows large but I have never heard of it getting to 7' tall. Mine never get beyond 4'.

Are you sure you do not have Hollyhock? That gets real tall and the flowers vary from deep dark purple looking almost black, to bright white and every color in between, usually in pinks but there are yellows too. It is a self seeder and may have gotten in from someones garden. If you do not like it where it is growing you can dig it up. It is a perennial so it will keep coming back if you do not dig it up.

Hollyhocks have beautiful flowers but the leaves always turn ratty and they look so raggedy in a garden. Every time I plant one I always get rid of it and say to myself "Never again".

Here is a link that might be useful: Hollyhock

Common Mullein gets very tall with yellow flowers...

Here is a link that might be useful: Common Mullein

Learning-as-i-go, can you post a photo? Then we can ID it without taking wild guesses based on your description?

I have seen people take a leaf/flower to the farmers market and ask farmers "Is this a weed?" They usually know.

Neighbors are always bringing me leaves/flowers to ID and asking me if it is a weed. I can ID if I see it.

You do not mention the suburb you live in but if you go to Plantland or Hawks, or one of the decent nursuries, someone who works there may ID it for you.