One of my students just called me half-panicked saying, “I am in retard! I am in retard!” Hmmm… I understood the basic idea – my student would not arrive on time. Unfortunately, her phrase makes very little sense in English and may even be offensive.
The word “retard” is short for “retarded” and is an offensive term for “mentally handicapped/challenged” person. As you can imagine, “I am in retard” sounds very strange.
To express this idea without sounding bizarre or offensive just say.
“I will be arriving late” – especially if you know in advance.
Ex: Next Tuesday I will be arriving late to our meeting because I have a doctor’s appointment before.
“I am running late” especially if you are in the process of being late.
Ex: Hello, I am on the subway and there’s a mechanical problem so I am running a bit late.