The Oxford English Dictionary and most scholars state that sincerity from sincere is derived from the Latin sincerus meaning clean, pure, sound (1525–35). Sincerus may have once meant "one growth" (not mixed), from sin- (one) and crescere (to grow).

Is the word sincere correct?

adjective, sin·cer·er, sin·cer·est. free of deceit, hypocrisy, or falseness; earnest: a sincere apology. genuine; real: a sincere effort to improve; a sincere friend.

Is sincerity the same as sincere?

The quality or state of being sincere; honesty of mind or intention; freedom from simulation, hypocrisy, disguise, or false pretense. ... Sincerity is everything. If you can fake that, you've got it made.