noun
substitute article; replacement item
A concrete object used in place of another, often in contexts like spare parts, stand-ins, or alternative products.
この部品の代替物はありますか。
Is there a substitute for this part?
代替品 is a near-synonym also meaning 'substitute product'; 代替物 is slightly more general and can refer to any replacement article, not necessarily a commercial product.
代わり is a broader, more common word for 'substitute' or 'replacement', used for people, actions, and objects. 代替物 is more formal and limited to physical items.
Compound of 代替 (だいたい, 'substitution') and 物 (ぶつ, 'thing'). The reading だいたい is the on'yomi of the kanji 代 and 替.