What are the special words in the Preamble of the Constitution and what is their meaning?

Preamble of indian Constitution

We, the people of India, to make India a [Sovereign Socialist Secular Democratic Republic], and to provide to all its citizens: justice, social, economic and political, freedom of thought, expression, belief, religion and worship, dignity and  To achieve equality of opportunity, and to increase fraternity ensuring the dignity of the individual and [ unity and integrity of the nation] among them all, in this Constituent Assembly today, November 26, 1949 AD (Miti Margashirsha Shukla Saptami,  Samvat 2006 Vikrami) hereby adopt, enact and surrender this Constitution.

These words attached in the preamble have special significance:

sovereign – 

socialist – 

The word was added by the 42nd Amendment Act of 1976.  It means social and economic equality.  Social equality means no discrimination on the basis of caste, colour, creed, sex, religion, language etc.  Everyone gets equal status and opportunities.  By economic equality it means that the government will strive for equitable distribution of wealth and provide a decent standard to all, hence the commitment in creating a welfare state.  Abolition of untouchability and Zamindari, Equal Wages Act and Child Labor Prohibition Act were some of the steps taken by the government in this context.

secular – 

The word was inserted by the 42nd Amendment Act of 1976.  Secular implies equality of all religions and religious tolerance.  No state in India has an official state religion.  Anyone can propagate, practice and propagate any religion of their choice.  In the eyes of the law, all citizens are equal regardless of their religious beliefs.  No religious instruction is given in government schools or government aided schools.

Democratic – 

This means that all levels of government are elected by the people through a system of universal adult franchise.  Every citizen of the age of 18 years and above, irrespective of caste, creed, colour, sex, religion or education, is entitled to vote, unless deprived by law.

republic –

 The term means that the head of the state is directly or indirectly elected for a fixed term.  The President of India is elected by the Electoral College for a fixed term of five years.