The word 'supersede' is sometimes misspelled as 'supercede'.
Another potential cause for confusion among some is the noun vs verb misspelling; e.g, 'practice' is a noun and 'practise' is a verb (i.e, to 'do' an activity), and ditto for advice (noun) vs advise (verb).
There's also 'cause vs 'cos, both shortened forms of the word 'because', then there's doughnut vs donut, and of course okay vs OK, though neither variation of each are actually wrong.