I dont think that those leaves are compound. Maybe one of the shrubby Lonicera?

Almost 100% certain they are compound. If you look closely in 2nd pic, you can see opposite leaf attachments (each leaf compound).

I think I see it now. Any chance it could be an Aralia?

Aralia spinosa

Funny, that's what I was thinking myself (there actually is an isolated woody Aralia near me on my neighbor's slope). But there aren't any nearby this plant AFAIK. I have a perennial spikenard (Aralia family), and tho its leaves are similar, its stems are fleshy and die off long before winter. This plant is in very deep shade, so perhaps that's part of the slenderness. But the slenderness might also suggest some kind of vine.

Thanks all. Whatever it is, it deserves a chance transplanted out in the sun somewhere.

Grab its stem really firmly with a bare hand. You'll soon learn to appreciate Devil's Walkingstick.

Depending on just how far away your neighbor's plant is, you may get to experience this species propensity to colonize anywhere its roots may venture. Then, you can transplant as many divisions as you could possibly want.