Lewis & Short

ex-pugnābĭlis, e, adj. [expugno], that may be taken, carried, or reduced by assault; expugnable (very rare): urbs terra marique expugnabilis est, Liv. 33, 17, 8: ne magnis quidem exercitibus, Tac. H. 3, 78: situ non expugnabile robur, Stat. Th. 6, 103: fluvius, i. e. exhaustible, id. ib. 4, 836.