X | meaning of X in Longman Dictionary of Contemporary English | LDOCE

From Longman Dictionary of Contemporary EnglishLetters & punctuation, Numbers, Maths, Education, Voting, Mail, FilmXX1, x /eks/ (plural X’s, x’s) noun    1 letter [countable, uncountable]SLA the 24th letter of the English alphabet2 HMNnumber [countable] the number 10 in the system of roman numerals3 mathematics [uncountable] technicalHM a letter used in mathematics to represent an unknown quantity or value  if 3x = 6, x = 24 on school workSEWRONG/INCORRECT [countable] a mark used on school work to show that a written answer is not correct5 when votingPPVCHOOSE [countable] a mark used to show that you have chosen something on an official piece of paper, for example when voting6 on a letterTCMKISS [countable] a mark used to show a kiss, especially at the end of a letter  Love, Cindy XXX 7 film [singular, uncountable]AMF used in the past to describe a film that was officially approved as only suitable for people over 18 SYN 18 → X-rated8 NAME OF A PERSONunknown/secret nameSECRET [uncountable] a letter used instead of someone’s or something’s real name because you want to keep it secret or you do not know it  At the trial, Ms X said that she had known the defendant for three years.9 when signing your nameSIGN YOUR NAME [countable] a mark used instead of a signature by someone who cannot write10 → X number of people/things11 → X marks the spotExamples from the CorpusX• Love, Cindy XXOXX• Suppose Mrs. X wants to make a donation. How can she be sure how her money will be used?• If 3x=6, then x=2.XX2 verb     → X something ↔ out