المعجم
al-Muʿjam
A collection of hadith whose items are arranged alphabetically, for example by the names of the Companions or the teachers.
What it means
Al-muʿjam is a collection of hadith arranged in alphabetical order. The usual arrangement is by the names of the narrators, such as the Companions or the compiler’s own teachers, which makes it easier to find reports. The best-known examples are the three Muʿjams of al-Tabarani: al-Kabīr, al-Awsaṭ and al-Ṣaghīr. The same word, muʿjam, came to mean a dictionary, since a dictionary also arranges its entries by the letters of the alphabet. The two meanings are linked by the principle of arrangement. Collections of this type are consulted by scholars as sources of reports and not as lists of verified material, because they contain reports of different grades.
Often misunderstood as
In modern Arabic the word is usually a dictionary, but in hadith study it is a collection arranged by names.
Term and Arabic as listed in Ismail al Faruqi, Toward Islamic English (International Institute of Islamic Thought, 1995), p. 50, listed as AL MU'JAM. The definition is restated here.