Hoon, in the Appletree Hundred of Derbyshire, is a simplex place-name from haugum, the dative plural form of Old Norse haugr ‘a natural height, a hill, a heap, an artificial mound, a burial mound’, which gives the sense ‘at the barrows’. One of these barrows is now called Hoon Mount.
Howsham, in the Yarborough Wapentake of Lincolnshire, is a simplex place-name from the dative plural of Old English hūs or Old Norse hús, both elements have the meaning ‘a house; also sometimes used of a building for special purposes’, so húsum ‘at the houses’. The weakly stressed -um was subsequently interpreted as -ham. This is a common formation in Denmark, so the place-name is likely Danish in origin.