“Congratulations” is the correct spelling. It is a plural form of the noun “congratulation” which means an expression of praise or approval for an achievement or good luck.
For example, “Congratulations on your graduation!” or “I extend my congratulations to the newlyweds.”
“Congratulation” is a singular noun and it is used less frequently in comparison to the plural form “congratulations.”
For example, “I offer my warmest congratulation to the winner.”
Adjective Degrees of Comparison List
