sub ‧ sti ‧ tu ‧ tion AC /ˌsʌbstəˈtjuːʃ ə n, ˌsʌbstɪˈtjuːʃ ə n $ -ˈtuː-/ BrE AmE noun [uncountable and countable]
[ Word Family: noun : ↑ substitute , ↑ substitution ; verb : ↑ substitute ]
when someone or something is replaced by someone or something else, or the person or thing being replaced:
Coach Ross made two substitutions in the second half.
substitution of something for something
the substitution of English for French as the world’s common language