'japonica' just means a plant from Japan, what 'japonica' is this you are asking about?

Just painting stump killer hasn't worked so try chipping out a groove between the bark and the trunk and put your stump killer down that. Then cover it with a piece of plastic and tie it on. You have to make sure the stump can absorb the liquid and just painting it on doesn't do it. It takes time.

To kill a tree we had, I drilled down into the stump and filled them up with Stump killer. I sealed the holes with mud.

Does not sound like a tree Steragram and Owdboggy, as Ellajack says taproot, which makes me think this is Fallopia japonica aka Japanese knotweed.

http://archive.defra.gov.uk/wildlife-pets/wildlife/management/non-native/knotweed.htm

http://www.environment-agency.gov.uk/homeandleisure/wildlife/130079.aspx

Its a fatsia japonica - Ellajack has put on another question with the name.

Ah - Did not expect that to grow vigorously back Steragram!

No - its surprising isn't it?

Just like to say thank you for the tips to rid me of this Japonica Fatsia plant.I have severed the roots from the main plant but cant dig the tap root out.I am a 65year old woman and cant dig it out.A few weeks ago i used a saw and an axe to chop into a branch.poured neat stump killer down it and around the roots,it grew new leaves but they have since died.the other half of it is still putting new leaves out. even after the stump treatment.Anyway i will perseverewith the stump killer or should i let it grow and keep chopping it to a managable height and width,Thank you all once again.

No use pouting stump killer onto the soil, it has to go onto the live wood and penetrate it. If you can stop the top from regrowing you can leave the root in - I'm older than you and that's what I do - a chestnut and a conifer both had huge roots and i just left them to rot. If you keep on killing the new growth it will give up eventually anyway.
(This sadly doesn't apply to sycamores...)

Thank you for that Steragram.I will do that