bap ‧ tis ‧ m /ˈbæptɪz ə m/ BrE AmE noun [uncountable and countable]
1 . a Christian religious ceremony in which someone is touched or covered with water to welcome them into the Christian faith, and sometimes to officially name them ⇨ christening
2 . baptism of/by fire a difficult or painful first experience of something:
The campaign has been a baptism of fire.
—baptismal /bæpˈtɪzm ə l/ adjective [only before noun] :
a baptismal font (=container for holding the water used at baptism)