capable of being taken or won by force: a pregnable fortress.
2.
open to attack; assailable: a pregnable argument.
Origin: 1400–50; late ME prenable < MF prenable, pregnable, equiv. to pren- (weak s. of prendre to seize, take < L pre(he)ndere;see prehension) + -able-able; -g- perh. from obs. expugnable (in same sense)
preg·na·ble (prěg'nə-bəl) adj. Being such that attack, seizure, or capture is possible; vulnerable or assailable: a pregnable fortress.
[Middle English preignable, pregnabul, from Old French prenable, pregnauble, from prendre, to grasp, from Latin prehendere, prēndere; see ghend- in Indo-European roots.] preg'na·bil'i·ty n.