Meaning of C in English

I. C 1 BrE AmE , c /siː/ noun ( plural C’s , c’s ) [uncountable and countable]

1 . the third letter of the English alphabet

2 . the first note in the musical ↑ scale of C ↑ major , or the musical ↑ key based on this note

3 . a mark given to a student’s work to show that it is of average quality

4 . the number 100 in the system of ↑ roman numeral s

II. C 2 BrE AmE

1 . the written abbreviation of Celsius or Centigrade :

Water boils at 100°C.

2 . written informal a way of writing ‘see’, used especially in emails and ↑ text message s :

CU (=see you) in class!

Longman Dictionary of Contemporary English.      Longman - Словарь современного английского языка.