impassable

From im- +‎ pass +‎ -able.

impassable (comparative more impassable, superlative most impassable)

1. (of a route, terrain, etc.) Incapable of being passed over, crossed, or negotiated.
   • 1960 December, “Talking of Trains: The railway and the Devon floods”, in Trains Illustrated, page 709:

     [...] at Cowley Bridge Junction, east of Exeter, both lines were impassable from about 1.30 p.m.—the first flooding of the junction for 36 years—and by the evening the water had risen two-thirds of the way up the platforms at St. Davids as Exeter faced its worst flooding for 60 years.

2. (of an obstacle) Incapable of being overcome or surmounted.
3. (of currency) Not usable as legal tender.

• unpassable

• impassible

From im- +‎ passable.

impassable (plural impassables)

1. impassable

• “impassable”, in Trésor de la langue française informatisé [Digitized Treasury of the French Language], 2012.