Gaml writes a plain g and continues the Semitic consonant behind the Hebrew gimel, the Syriac gamal and the Arabic jim. The Arabic member of the set shows a sound change: the inherited g became j in the standard language, though several dialects, Egyptian among them, keep the g.
The name is one of the small group in the fidel whose sense is still visible. It is the Semitic word for a camel, gamal in Ge'ez as in Hebrew, and the letter is named acrophonically for it in the same way the Canaanite alphabet named its signs. Bet and res are the other clear cases. Beyond those three the Ge'ez names have worn down and no meaning is recorded for them here.
Gaml also heads one of the labiovelar series, so there is a rounded counterpart of this letter written as a sign of its own and carrying five orders rather than seven. That is a detail of the writing system rather than of the alphabet, and the atlas keeps the two apart: the alphabet is the twenty-six consonants the tradition recites, and the writing system is the larger inventory that has grown around them to serve Ge'ez, Amharic, Tigrinya and Tigre together.
Ethiopian Semitic did not make that change, so a Ge'ez word and its Arabic cognate can look further apart than they are. Recognising that a j in Arabic answers to a g elsewhere in the family is one of the first adjustments a reader moving between the two languages has to make, and it is exactly the sort of regular correspondence a comparative dictionary exists to record.