According to Alexander Beider in his book "A Dictionary of Jewish Surnames from the Russian Empire", the name Dekelbaum was found in Pinsk (in Minsk), and Rovno (Volhynia), whereas the spelling Dekelbojm occured in Rovno, and was common in Lutsk (Volhynia).

Dekel or deqel is the Hebrew word for palm tree, although, the Hebrew word used for palm tree in the Bible is tamar. The word baum or boim or bojm has the meaning of tree, although not precisely palm tree. According to my learned Uncle Bernie (Rabbi Leffell), the dekel or tamar was regarded as being tall and straight, so it is likely that the person who was first given that name was a tall man, perhaps with good posture.

You may ask yourself (as I did), how did the Jews in the Ukraine know from palm trees? Again Rabbi Leffell tells me that they knew about palm trees from their study of the Bible and Rabbinic Literature and from their observance. For example, in preparing for Sukkot, the Torah instructs (Leviticus 23:40) "........ you shall take...... branches of palm trees.....". These, together with the etrog (citron), were imported then as now.