Dip thy morsel in the vinegar - The חמץ chomets, which we here translate vinegar, seems to have been some refreshing kind of acid sauce used by the reapers to dip their bread in, which both cooled and refreshed them. Vinegar, rob of fruits, etc., are used for this purpose in the East to the present day; and the custom of the Arabs, according to Dr. Shaw, is to dip the bread and hand together into these cooling and refreshing articles.
Parched corn - This was a frequent repast among the ancients in almost all countries; see the notes on Leviticus 2:1-14; (note).
To dip the morsel, or sop, whether it were bread or meat, in the dish containing the vinegar (compare Matthew 26:23; Mark 14:20: Exodus 25:29; Numbers 7:13) was, and still is, the common custom in the East.
Parched or “roasted” corn - Grain was the common food of the country then (compare 1 Samuel 17:17; 1 Samuel 25:18; 2 Samuel 17:28) as it is now.
And left - Or “reserved” Rth 2:18 . Rather, “had some over” (compare Luke 15:17). Rth 2:18 tells us that she took to her mother-in-law what she had left over.