So, are those two words related? If so, how? Is one native and one a loan-word? Or are both loan-words? If so, from which language(s)?
1 Answer
Sūd- means "dry" rather than "bright", and might be cognate with English "sere" or might come from sē- "without" + ūd- "wet".
Sīder- is of uncertain etymology, but there's no real reason to connect it with the word for "dry". The two roots don't look especially similar phonetically.