This paper explores the elision of the excessive letter in two derivations in Arabic morphology, namely: the gerund and the participle. In his great lexicon: Al-Muhkam wal-Muheet ulA'adham the outstanding linguist Ibnu Seeda al-Andalusi. Ibnu Seeda used two terms related to the excessive letters; they are: "elision" and "subtractions" and he suggested elision of the excessive letter in the gerund and the participle. In the examples he presented, Ibnu Seeda suggested the omission of the excessive letters.