1) Apt to morph 2) Chameleonlike 3) Changeable 4) Constantly changing 5) Given to changing 6) Inconstant 7) Not set in stone 8) Tending to change Found on https://www.crosswordclues.com/clue/mutable
• (a.) Capable of alteration; subject to change; changeable in form, qualities, or nature. • (a.) Changeable; inconstant; unsettled; unstable; fickle. Found on http://thinkexist.com/dictionary/meaning/mutable/
Mu'ta·ble adjective [ Latin mutabilis , from mutare to change. See Move .] 1. Capable of alteration; subject to change; changeable in form, qualities, or nature. « Things of the most accidental and mutable nature.» South. 2. Changeabl... Found on http://www.encyclo.co.uk/webster/M/121
an attribute of a member that makes it possible to change its value even if its object is declared to be const TC++PL 10.2.7.2, D&E 13.3.3. Found on http://www.stroustrup.com/glossary.html
adjective capable of or tending to change in form or quality or nature; `a mutable substance`; `the mutable ways of fortune`; `mutable weather patterns`; `a mutable foreign policy` Found on https://www.encyclo.co.uk/local/20974
liable or subject to change or alteration. · given to changing; constantly changing; fickle or inconstant: the mutable ways of fortune. Found on https://www.infoplease.com/dictionary/mutable