Optimum (4)
(Other definitions for acme that I've seen before include "Top or highest point" , "Height of excellence" , "'Highest point, apex (4)'" , "Height of perfection" , "Summit of achievement" .)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">optimum</span>' is the definition.<br/ ><span class="explanation-format__explanation">(similar in meaning)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for best that I've seen before include "Superlatively good" , "Worst -- as good as can be" , "12 21[FOOTBALLER" , "Most advantageous" , "erstwhile drummer" .)