(n.) An invariable quantity; specifically, a function of the coefficients of one or more forms, which remains unaltered, when these undergo suitable linear transformations.

abiding accordant alike automatic balanced blah broken-record changeless consistent consonant constant continuous correspondent drearisome dreary dry dryasdust dull dusty enduring equable equal eternal even everlasting fast fixed flat harping homogeneous humdrum immovable immutable inalterable incommutable inconvertible indefeasible inert inflexible insusceptible of change intransmutable invariant irretrievable irreversible irrevocable jog-trot lasting level long-winded measured mechanical methodic monolithic monotonous noble nonreturnable nonreversible of a piece ordered orderly permanent persistent prolix regular reverseless rigid robotlike set singsong smooth stable steadfast steady systematic tedious treadmill unalterable unalterative unaltered unbroken unchangeable unchanged unchanging undeflectable undeviating undifferentiated undiversified uneventful unexceptional unfailing uniform unmodifiable unmodified unmovable unremitting unrestorable unreturnable unruffled unsusceptible unvariable unvaried unvarying unwavering