The most common and most likely answer to this crossword clue is the 6 letter word OTTAWA
I've seen this crossword clue in The Daily Telegraph
O
T
T
A
W
A
More clues leading to the result OTTAWA
- Ring a Scottish engineer up in capital
- City of old to which a measure of power returns
- At two, travelling by a capital city
- Semi-aquatic mammal picked up north of Washington capital
- Some boycott a warmonger: capital!
- From nothing, a power unit raised capital
- Ordinary power returns to a capital
- Ring up a Scottish engineer in 21’s capital
- Federal capital to put up tall wall to exclude students
- Canadian city very much distant? Not entirely
Buddy explains!
The straight part
We know that "capital" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case capital = ottawa.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.