Hello and welcome!
Tump is a mound, usually artificial, the word appears quite a lot in Herefordshire (Wormelow Tump, Aston Tump, etc) and sometimes gets applied to mottes.
I think it must also be related to Twmpa, the Welsh name of one of the peaks in the Black Mountains - the English version is the more Viz-friendly Lord Hereford's Knob. Twmpa is pronounced "Tumpa" or "Toompa".