This is the 11816th most frequent Russian word.
заменой
"Заменой" means "replacement" or "substitution."
In this sentence, 'заменой' is used as a noun in instrumental case to denote 'as a replacement' or 'by way of replacing'.
Эта деталь идеально подходит как заменой старой.
This part is perfect as a replacement for the old one.
Here, 'заменой' functions as an instrumental describing the substitution offered in place of something else.
Учитель предложил книгу в качестве заменой пропущенной лекции.
The teacher suggested the book as a substitute for the missed lecture.
'Заменой' acts as an instrumental noun, indicating the entity taking the place of or substituting.