Principal city (7)
I believe the answer is:
capital
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">principal city</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 capital that I've seen before include "Topping" , "Upper-case letter" , "A great city - that's fine" , "Cardinal; splendid; assets" , "(Person's) wealth" .)