Lord Kartikeya is also known as Swaminatha and there is good reason behind that.
Once Kartikeya asked Lord Brahma the meaning of Om. Brahma tried to explain to him but he was not satisfied.
Later on, when Lord Shiva queries, he explained the whole episode to him. Lord Shiva told that he must learn from Lord Brahma, as he is the supreme creator.
Lord Kartikeya said that then Lord Shiva should explain him the meaning of Om.
Hearing this, Lord Shiva smiled and said, ‘Even I don’t know.’ Kartikeya then said, ‘Then I will tell you because I know the meaning of Om.’
Lord Shiva: ‘Then tell me the meaning since you know it’
Kartikeya: ‘I can’t tell you like this. You have to give me the place of the Guru. Only if you put me on the pedestal of the Guru can I tell you’, said Kartikeya.
Lord Shiva thought that Guru means he has to be in a higher position or platform. The teacher has to sit on a higher place and the student has to sit down and listen to him. But how can I find a seat higher than him, for he is the highest and greatest of Gods?’
So then Lord Shiva lifted the young Kartikeya on to His shoulders. And then in the ear of Lord Shiva, Lord Kartikeya explained the meaning of the Pranava Mantra (Om).
Kartikeya: ‘That the entire Creation is contained in Om. The Trinity – Lord Brahma, Vishnu, and Shiva are contained in Om. This is the essence and also the secret of Om that Lord Kartikeya narrated to Lord Shiva.’
Upon hearing this, Goddess Parvati (Mother of Lord Kartikeya, and an incarnation of the Mother Divine) was elated and overcome with joy.
Goddess Parvati: ‘You have become a Guru (Swami) to my Lord (Natha)!’
Saying this she addressed her son as Swaminatha, and ever since Lord Kartikeya also came to be known as Swaminatha.