From over- + nimble. <span class="searchmatch">overnimble</span> (comparative more <span class="searchmatch">overnimble</span>, superlative most <span class="searchmatch">overnimble</span>) Excessively nimble. 1648, Thomas Fuller, The Holy State, page...
Fuller, The Holy State, page 167: Acquaint thy self by degrees with hard and knotty studies, as School-divinity, which will clog thy <span class="searchmatch">overnimble</span> Phancie....