I think the Turkish cap has to be spelt with a 'C'...ie calpac. If it isn't, I'm wrong with 21 across! The 'c' comes from that old crossword trick of using the word 'see' as code...ie sounds like 'c'.
The reason it's spelt 'see', Ich, is precisely because it sounds like 'C'! In the same way, 'tee' is that letter's name because it makes the appropriate sound. The word 'tee' in a clue, therefore, might mean the letter, a golfer's peg, the target in curling etc.