that cannot be reversed or revoked

irrevocable

final and unalterable

fixed, unchangeable

not expected to change; going on for a long time; intended to last

constant, lasting

stiff; that cannot be bent; firm; strict; not changing

stiff, strict, severe

firmly fixed; loyal

loyal, steady

firmly fixed or supported; not likely to fall over; not changing in amount, speed etc; (of a person behaviour) having, keeping to, a regular (good) pattern

stable, fixed

having good reasons to believe something; free from doubt; proved; reliable; without a doubt

certain, definite