Conversation so far:
What rewards did Vasco da Gama receive?
Vasco da Gama received the town of Sines as a hereditary fief in December 1499
What happened with the town of Sines after Vasco da Gama received it as a hereditary fief?
Vasco da Gama receiving Sines turned out to be a complicated affair, for the town still belonged to the Order of Santiago.
What happened after Vasco da Gama received Sines the town that still belonged to the Order of Santiago?
the fact that Sines was awarded to Vasco da Gama by the king provoked Lencastre to refuse out of principle, lest it encourage the king to make other donations of the Order's properties.
What did Vasco da Gama do with Sines after provoked Lencastre to refuse out of principle lest it encourage the king to make other donations of the Order's properties?
Vasco da Gama would spend the next few years attempting to take hold of Sines, an effort that would estrange him from Lencastre
What else was da Gama doing at this time aside from attempting to take hold of Sines, an effort that would estrange him from Lencastre?
In the meantime, da Gama made do with a substantial hereditary royal pension of 300,000 reis.
Was da Vasco da Gama rich?
Vasco da Gama made do with a substantial hereditary royal pension of 300,000 reis.
What other things was da Gama involved in aside from having a substantial hereditary royal pension of 300,000 reis?
Vasco da Gama was awarded the noble title of Dom in perpetuity for himself, his siblings and their descendants.
Were there any other rewards given besides the noble title of Dom in perpetuity for himself, his siblings and their descendants?
On 30 January 1502, Vasco da Gama was awarded the title of Almirante dos mares de Arabia, Persia, India e de todo o Oriente
What does this title Almirante dos mares de Arabia, Persia, India e de todo o Oriente mean?
Almirante dos mares de Arabia, Persia, India e de todo o Oriente  means Admiral of the Seas of Arabia, Persia, India and all the Orient“

Question: What is the origin of this title?
Self-contained rewrite: What is the origin of this title Admiral of the Seas of Arabia, Persia, India and all the Orient?