When describing someone who is deep in thought or intensely focused on something, there are many synonyms for the phrase "absorbed in." These synonyms include engrossed, immersed, captivated, enthralled, fascinated, preoccupied, lost in, and entranced. Each of these words carries a slightly different connotation, but all convey the idea of complete absorption or concentration. When choosing a synonym for "absorbed in," it often depends on the context and tone of the sentence. For example, "entranced" might be more appropriate for describing someone's fascination with a beautiful piece of music, while "preoccupied" might be better suited for someone who is deeply worried about a problem.