Is SIDER a Wordle Word?

Yes. SIDER is a valid Wordle word.

It is not on the Wordle answer list, so it is unlikely to be a daily answer.

What does SIDER mean?

One who takes a side.“enemies of God and our Religion, and siders with Antichrist”
A shape with a specified number of sides.
Obsolete form of cider: An alcoholic, often sparkling (carbonated) beverage made from fermented apples.

Definition from Wiktionary, available under the CC BY-SA license.

Starter word rating: GoodIn the top 7% of all valid Wordle words for testing common letters.
Vowels: I, E
Unique letters: 5 of 5
Common letters: I, E, R

Hard-mode trap: 8 valid words fit the pattern _IDER. If you reach it, you may need several guesses to find the last letter.

Letter ratings use how often each letter appears in Wordle answers.

Tap its tiles to the colours Wordle showed, and the Wordle Solver lists every word that still fits, with the best next guess.