As verbs the difference between tumb and tump
is that
tumb is (archaic) to tumble; jump; dance while
tump is to form a mass of earth or a hillock about or
tump can be (southern us) to bump, knock (usually used with "over", possibly a combination of "tip" and "dump").
As a noun tump is
(british|rare) a mound or hillock or
tump can be (uncommon) a tumpline.