A.T. Robertson Commentary Matthew 22:4

"Again he sent forth other servants, saying, Tell them that are bidden, Behold, I have made ready my dinner; my oxen and my fatlings are killed, and all things are ready: come to the marriage feast." — Matthew 22:4 (ASV)

My dinner (το αριστον μου). It is breakfast, not dinner. In Lu 14:12 both αριστον (breakfast) and δειπνον (dinner) are used. This noon or midday meal, like the French breakfast at noon, was sometimes called δειπνον μεσημβρινον (midday dinner or luncheon). The regular dinner (δειπνον) came in the evening. The confusion arose from applying αριστον to the early morning meal and then to the noon meal (some not eating an earlier meal). In Joh 21:12,15 αρισταω is used of the early morning meal, "Break your fast" (αριστησατε). When αριστον was applied to luncheon, like the Latin prandium, ακρατισμα was the term for the early breakfast.

My fatlings (τα σιτιστα). Verbal from σιτιζω, to feed with wheat or other grain, to fatten. Fed-up or fatted animals.