Some words that start with C and end with U are:
clement
A five letter word with the third letter O and the last letter C is stoic.
clasping
c is the first letter of "commission" , which is probably the word you have in mind.
contract
accedeicicleoctaneoctaveScythe
mac
icon, scan
Tragic
C is the first letter in the word Civil.
The word, circle has both a soft and a hard consonant. The first letter "c" is a soft consonant and the last letter , "c" is a hard consonant. That makes the first letter , "c" sound like the letter, "s", while the second letter, "c" sounds like the letter, "k".
c (commission)