Is CEILS a Wordle Word?

Yes. CEILS is a valid Wordle word.

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

Plurals ending in S are almost never chosen as Wordle answers.

What does CEILS mean?

To line or finish (a surface, such as a wall), with plaster, stucco, thin boards, or similar.
To set a higher bound.

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

Starter word rating: GoodIn the top 10% of all valid Wordle words for testing common letters.
Vowels: E, I
Unique letters: 5 of 5
Common letters: E, I, L

Hard-mode trap: 8 valid words fit the pattern _EILS. 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.