Riddle #634

Question: I am a nice word composed of five letters, but the Romans would call me a numbers.

What am I?

Question: What do you call a sad bird?

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Question: What can be broken but never forgotten?

Question: What tastes better than it smells?

Question: People see through me, but none pass through without killing me. I can be anywhere, and can be seen double or single. What am I?