COMMUTABLE
commutable
(adjective) subject to alteration or change; “the death sentence was commutable to life imprisonment”
commutable, substitutable
(adjective) capable of being exchanged for another or for something else that is equivalent
Source: WordNet® 3.1
Etymology
Adjective
commutable (comparative more commutable, superlative most commutable)
Capable of being commuted.
Source: Wiktionary
Com*mut"a*ble, a. Etym: [L. commutabilis.]
Definition: Capable of being commuted or interchanged.
The predicate and subject are not commutable. Whately.
Source: Webster’s Unabridged Dictionary 1913 Edition