Upper-case letter (7)
I believe the answer is:
capital
'upper-case letter' is the definition.
(synonyms)
This is all the clue.
(Other definitions for capital that I've seen before include "liquid assets" , "Major city - investment - great!" , "Kabul or Harare?" , "A big letter, or a big city" , "It's jolly good in the great city" .)