The phrase "am on horizon" suggests the idea of something coming into view or approaching. When considering antonyms for this phrase, the opposite concepts may include the idea of receding, disappearing, or moving away. Words such as "receding," "departing," or "fading" could all be used as antonyms for "am on horizon." These words suggest an element of distance or separation, rather than convergence or advancement. Other antonyms may include "disappearing," "vanishing," or "dissolving." Ultimately, the choice of antonym will depend on the context and intent of the phrase, as well as the particular nuance that is being emphasized.