/ ɪmˈpregnəbl; NAmE / adjective
1.
an impregnable building is so strongly built that it cannot be entered by force :
an impregnable fortress
2.
strong and impossible to defeat or change
SYN invincible :
The team built up an impregnable 5-1 lead.
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WORD ORIGIN
late Middle English : from Old French imprenable , from in- not + prendre take (from Latin prehendere ). The current spelling arose in the 16th cent., perhaps influenced by Old French variants.