Meaning
to be an authority in; be an expert in; to study thoroughly; to delve deeply into
Example
أَنَّهُ كَانَ مِنْ أَكْثَرِ النَّاسِ تَبَحُّرًا فِي الْفَلْسَفَةِ He was one of the most knowledgeable people in philosophy.
Notes
تَبَحُّر (في) - deep knowledge