Correct spelling


Correct spelling, explanation: superseded is a past-tense form of a base word supersede with an -ed suffix, which here is shortened to just d, as the e is already at the end. The spelling of the base word is dictated by its origin, which is the Latin word supercedere, and as a rule, the structure (so the consonants) of the word is not changed without a good reason.

Definition of superseded:
verb, past tense of supersede
1. to take place of something else
For me, the need to have money to pay rent supersedes the need to buy a new car.
Old human beliefs about nature were eventually superseded by scientific facts.

Incorrect spelling


Incorrect spelling, explanation: the pronunciation of superceeded would be correct, but the spelling is wrong. The original word here is Latin supersedere – and while the word became slightly adjusted to look and sound more English – supersede – changing sede to ceede is simply unnecessary and unsubstantiated, which is why superseded is the only correct spelling.