temerity (n.) Look up temerity at Dictionary.com
late 14c., from Latin temeritatem (nominative temeritas) "blind chance, accident; rashness, indiscretion, foolhardiness," from temere "by chance, at random; indiscreetly, rashly," related to tenebrae "darkness," from PIE root *teme- "dark" (cognates: Sanskrit tamas- "darkness," tamsrah "dark;" Avestan temah "darkness;" Lithuanian tamsa "darkness," tamsus "dark;" Old Church Slavonic tima "darkness;" Old High German dinstar "dark;" Old Irish temel "darkness"). The connecting notion is "blindly, without foreseeing."