Namo is to direct your mind to 'Bhagavaa araha.m sammaasambuddho'.
It is usually accompanied by verbal and bodily action.
More accurate, namo is the personification of the action of Vandanaa.
Tassa is literally to that; it indicates that the person is not in the presence of Bhagavaa...
Bhagavaa is how the disciples addressed him. It means Lord and is the standard Indian way of referring to Guru (Religious teacher) or Satthaa in Pali.
Araham is and indication of absolute purity of Bhagavaa...He is worthy of worship by everybody without exception.
Sammaasambuddho-Sammaa means only, unique, right perfect etc. He is only equal to himself. It is Bhagavaa's knowledge. Also sammaa di.t.thi...sammaa samaadhi is the Ariyoa.t.tha,ngikomaggo (The Aryan Eightfold Path) discovered by Samana Gotama--Majjhimaa Pa.tipadaa. Its realisation made him the Sammaasambuddho.
Bhagavaa is usually defined in the following expression: Itipi so Bhagavaa araham sammaasabuddho, vijjaacaranasampanno sugato lokavidu anuttaro purisadhammasaarathii satthaa devamanussaana.m buddho bhagavaati.
The three words are necessary and sufficient to identify the class of 'beings' called bhagavaa araha.m sammaasambuddho.
Simply put A teacher whose purity and knowledge is absolute.
With friendly thoughts,