suffix
substitute for; in place of
Attaches to nouns to mean 'instead of' or 'as a substitute for'. Often used in compounds like 身代わり (substitute person) or 親代わり (acting as a parent).
彼は親代わりに弟の面倒を見ている。
He takes care of his younger brother in place of their parents.
この薬は砂糖代わりに使える。
This medicine can be used as a substitute for sugar.
The noun 代わり (かわり) means 'substitute' or 'replacement' and can stand alone, while がわり is a suffix that attaches to other nouns.
Derived from the noun 代わり (かわり), with rendaku voicing to がわり when used as a suffix.