The word "un-detected" refers to something that has not been discovered or noticed. Its antonyms are words that have the opposite meaning. Some antonyms for "un-detected" include "discovered," "found," "noticed," "seen," and "spotted." These words suggest that something or someone has been observed or identified. Other antonyms include "visible," "obvious," "apparent," and "evident," which imply that something is easily seen or noticed. The opposite of "un-detected" can also be expressed by words like "caught," "exposed," "revealed," and "unmasked," which suggest that something has been uncovered or made public.