The most frequent word in the Hebrew texts is ironically a word never translated and left out of translations.
This is because it is unknown. It has mystified scholars for centuries and there have been speculations and educated guesses (i.e. a mark of the accusative) ever since Rabbi Akavi of the 1st century CE who labeled it a “mark of the divine hand”. It is peculiar that a word which makes up 10% of all the nouns in the text ends up left out of the translation process altogether. The two letters aleph and tav are curiously the first and last letters of the Hebrew alphabet. Many further speculations are built around this fact. Most of the occurrences are found in the Pentateuch, the first five books of Moses.