Definify.com

Webster 1913 Edition

Adj.

Being, or capable of being, a matter of opinion; that can be thought; not positively settled;

as, an

opinionable

doctrine

C. J. Ellicott.

opinionable ‎(comparative more opinionable, superlative most opinionable)

Being a matter of opinion; not positively settled.
- Charles John Ellicott, Bishop of Gloucester
  […] a time like the present, when there is such a distinct tendency to consider everything as opinionable […]