From détestable + -ment. <span class="searchmatch">détestablement</span> detestably “<span class="searchmatch">détestablement</span>”, in Trésor de la langue française informatisé [Digitized Treasury of the French Language]...
at something (detestable) méprisable (bad at something) lamentable <span class="searchmatch">détestablement</span> “détestable”, in Trésor de la langue française informatisé [Digitized...