The prayer Ashrei (which is Psalm 145) is recited during services three times a day. One of the most noticeable features of Ashrei is that it is an acrostic of the entire Hebrew alphabet, with the letters of the aleph-bet, in order, starting each line except one. The line that should have begun with the letter nun, is missing. From aleph to tav, all the other letters are accounted for. According to the Talmud (Berachot 4b), “Rabbi Johanan says: Why is there no nun in Ashrei? Because the fall of Israel begins with it. For it is written: ‘Fallen is the virgin of Israel, she shall no more rise’ (Amos 5:2).” The letter nun is skipped because it represents the concept of falling (Nun-Phey-Lamed).
On the other hand, nun is also the letter that begins such words as neshama (soul) and ner (candle). The neshama is often compared to a ner, representing the way that the soul guides a person through the turmoil of life.
When used as a prefix with a verb, nun signifies the first person plural future (we) conjugation. According to The Wisdom in the Hebrew Alphabet, when used as a suffix the nun can signify the superlative, adding intensity to a description or causing a noun to be transformed into an adjective. For instance, rachaim means “have mercy,” but rachman means a compassionate person.
The nun is one of the five letters that uses a sofit form. The regular nun sits on the same line as the other numbers, whereas the nun sofit is long, dropping down well below the other letters.
Numerically, the letter nun is equivalent to 50.
Bibliographical acknowledgment: The Wisdom In The Hebrew Alphabet: The Sacred Letters as a Guide to Jewish Deed and Thought. By Rabbi Michael L. Munk. Published by Mesorah Publications, 1983.