That cannot be achieved (or only with great difficulty)
unavouchable
unavouchably
unconvenable
unconveyable
unconveyable
adj
Impossible to convey.
uncultivable
uncultivable
adj
Not capable of cultivation
undeceivable
undeceivable
adj
Not deceivable.
undeceivably
undeceivably
adv
In an undeceivable way.
uninvincible
uninvincible
adj
(rare) Not invincible.
uninvincibly
unreceivable
unvindicable
unvindicable
adj
Not vindicable.
vibratiuncle
vibratiuncle
noun
(now chiefly historical) A minuscule or slight vibration; specifically, a vibration in brain tissue caused by the comparatively greater vibrations of the particles of the medullary substance of the nerves (formerly hypothesised to convey external impressions to the mind).