fathom

This word carries a heavy sense of intellectual struggle. It is rarely used for simple understanding; instead, it describes the process of grasping something that feels alien, illogical, or profoundly deep. Using this word suggests that the subject is a puzzle or a mystery that resists easy comprehension. In its original nautical sense, it describes the physical act of probing the depths. This physical imagery persists in its mental usage, where the mind is seen as diving deep into a complex problem to find the bottom or the truth. It is more formal than understand and more emotive than comprehend.