This word is acceptable for play in the US & UK dictionaries that are being used in the following games:

• Lexulous
• Wordscraper
• Wordosaur

ad. In a way that cannot be varied, or changed.

So as not to suffer change; without change; immutably.

ad. in an unalterable and unchangeable manner

"The Chicago church where President Obama belonged for 20 years, Trinity United Church of Christ, is theologically liberal, eschewing scriptural inerrancy and taking apostolic creeds as "testimonies" of faith, rather than literally, unchangeably true."

unalterably    immutably