They are similar, but each word has its nuanced meaning. Explicit: clear, literal, not hidden. Unambiguous: The meaning of something cannot be questioned/the intention of the writer is clear. I hope that helps :)

"Explicit" means to purposefully express, with the intention of being "unambiguous". 'Unambiguous" versus "Confused" "Explicit" versus "Nuanced"/"Subtle" It is sometimes easier to understand a word by looking at its antonyms as well as its synonyms.