Definition of supersession in US English:

supersession

noun

  • Replacement of a person or thing previously in authority or use.

    ‘declining health caused his resignation and supersession by Baldwin’
    ‘the supersession of the Old Covenant with the New’

Pronunciation

supersession

/ˌso͞opərˈseSH(ə)n//ˌsupərˈsɛʃ(ə)n/