A principle to be aimed at (5)
I believe the answer is:
ideal
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">a principle to be aimed at</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for ideal that I've seen before include "Perfectly suited" , "Dream" , "Optimum" , "Perfect but perhaps unlikely to become reality" , "Embodying perfection" .)