unventableadj.
Etymology: Previous versions of the OED give the stress as: unˈventable.
the mind > emotion > [adjective] > not able to be expressed
1633 T. Adams (ii. 4) 533 But O..the unventable sorrow of the goates on his left!
This entry has not yet been fully updated (first published 1926; most recently modified version published online June 2019).