sincero
/sinˈθeɾo/ · A2 · adj
sincere
sincero = sincere with an -o; same Latin root, sincerus (pure, genuine)
A direct cognate of English sincere, both from Latin sincerus meaning clean, pure, unmixed. Swap the final -e for -o (sincera for feminine). In Spain the c is a soft th sound: seen-THEH-ro.