एकदन्तम् (ekadantam) ...

एकदन्तम् महाकायम्
तप्त काञ्चन सन्निभम्।
लम्बोदरम् विशालाक्षम्
वन्देहम् गणनायकम्॥

ekadantam mahAkAyam
tapta kAncana sannibham |
lambodaram vishAlAksham
vandeham gaNanAyakam ||

एकदन्तम्  - single tusked
महाकायम् - one with a mighty body
तप्त  - melted (molten)
काञ्चन  सन्निभम् - like gold
लम्बोदरम्  - having a large tummy
विशालाक्षम् - having very large eyes
वन्देहम्  गणनायकम् - I bow down to you Lord Ganesha

O’ single tusked Lord, One with a mighty body as if made of molten gold, One with a very large tummy and One with large eyes, I bow down to you!

The popular theory for Lord Ganesha having one of his tusks broken is that he broke it off to use it as a pen to script the epic Mahabharatha. Another less known story is the following: Parashurama, the son of Sage Jamadagni became a disciple of Lord Shiva and a co-student of Ganapati. After completing his studies, on account of his utter rage against Kshatriyas (rulers), he trotted the globe 21 times and destroyed them all. After this, he went to Kailasa. He crossed all the doors of Lord Shiva's palace. Ganapati was guarding the last door which lead to Shiva's personal chamber. Ganapati refused to let Parashurama in saying that it was Shiva's resting time. Parashurama argued that he was like a son to Shiva and that he had all the right to go inside. Heated exchange of words took place. Parashurama, still raging with anger, assaulted Ganapati on his tusk. Ganapati too became angry and lifted Parashurama with his trunk, spiralled him high in the air and dumped him on the ground and finally drowned him in the seven seas. This act of Ganapati accorded atonement to Parashurama for his cruel deed of slaying the rulers. After repeating this several times, Ganapati finally dumped Parashurama on the ground again. Parashurama, failing to appreciate the fact that Ganapati had infact purified him of his sins, launched the Parashu (a weapon which Lord Shiva had given him) on Ganapati. Ganapati did not want to insult the weapon given by his father to Parashurama and thus offered his left tusk to it. The weapon broke the tusk. Parvati came out. An ambassador came from the Vishnu loka and pointed out the foolish behaviour of Parashurama and condemned it. Parashurama realised his mistake and immediately fell at the feet of Parvati Devi and begged to be forgiven.This is the story of how Gajanana became Ekadanta.