Chi
Chi is a three-letter word that identifies both a Greek letter and an abbreviation for Chicago. It is the twenty-third letter in the Greek alphabet. It also represents the IATA (International Air Transport Association) code for all airports in Chicago, Illinois.
X comes from the Greek letter Chi, which is the first letter in the Greek word which means Christ.
The abbreviation for nanometer is "nm". No Greek letters are used in this case.
pi is not an abbreviation. It is a letter of the Greek alphabet symbol that symbolises one particular ratio.
chi.
psych, psy, psyc, or ψ (the greek letter psi)
I don't believe that there is an abbreviation for Chicago.
The abbreviation for Chicago is Chgo.
It is disrespectful only if you mispronounce it Eksmas. In the abbreviation Xmas (pronounced "Christmas"), the X- is not the Roman letter x. It is the Greek letter chi, which is long-established as a proper abbreviation for Christ.
the abbreviation is T
The Greek letter delta is the medical symbol for change. It's a little equilateral triangle.
Chi