also: かけかえ
noun
replacement; substitute; rebuilding; changing
Refers to something that can replace or be substituted for another, often used in the phrase かけがえのない (irreplaceable).
家族はかけがえのない存在だ。
Family is an irreplaceable presence.
この経験はかけがえのないものになった。
This experience became something irreplaceable.
Kanji spelling using 替 (replace); restricted to reading かけがえ.
Alternate kana spelling reflecting the reading かけかえ; rarely used.
Alternate kanji spelling using 変 (change); reading かけかえ is less common.
代わり is a more common and general word for substitute or replacement, while かけがえ is often used in the set phrase かけがえのない to emphasize irreplaceability.
Compound of 掛け (kake, continuative form of 掛ける 'to hang, set') + 替え (kae, continuative form of 替える 'to replace'). The exact historical derivation is uncertain, but the meaning of 'replacement' is conventionally associated with these components.