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to garnish; to accompany (as a card does a gift)
to add to as support; to prop up
to accompany (as an aid, guide, translator, etc.)
手紙にメッセージカードを添えた。
I enclosed a message card with the letter.
レストランでメイン料理に彩りのパセリを添えて出した。
I served the dish garnished with parsley.
贈り物には感謝の気持ちを一言添えるのが日本の礼儀だ。
It's polite to add a word with a gift.