I recently came across an interesting false friend in the form of the word scrupulous, providing great potential for thorough confusion.
According to Merriam-Webster, scrupulous means, in particular,
having moral integrity, acting in strict regard for what is considered right or proper.
Its opposite is unscrupulous. As a German native speaker, I find that quite interesting because the German word skrupellos looks and sounds very much like scrupulous (pronounced [ˈskruːpjələs], listen here) but actually means unscrupulous (see here)!
German translations of unscrupulous include
gutmütig, mitfühlend, rücksichtsvoll.
Hence, both the English scrupulous and the German skrupellos can be false friends and you should take scrupulous care to use them right.