light, brightness, clarity
Something that is pellucid is either extremely clear because it is transparent to the eye or it is very easy for the mind to understand.
If you elucidate something, you make it easier to understand by giving more relevant information.
If someone is lucid, they are able to understand things and think clearly; this adjective is especially used when someone was not always able to do this because of illness or confusion.
A translucent object allows some light to pass through it.
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