Webster's English Dictionary

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impermeable

im.per.me.able \(')im-'p*r-me--*-b*l\ \-ble-\ aj [LL impermeabilis, fr. L 
   in- + LL permeabilis permeable] : not permitting passage (as of a fluid) 
   through its substance : IMP ERVIOUS - im.per.me.able.ness n