deep

The primary image is one of distance from a surface—whether that surface is physical (water), auditory (pitch), or psychological (consciousness). When applied to emotions or thought, it suggests a layer of complexity and seriousness. It differs from 'intense' by implying a verticality; something deep isn't just strong, it has roots or foundations far below the visible exterior. In a physical sense, it conveys a feeling of immersion or being enveloped. When used as an adverb, it emphasizes penetration into the heart of a space, moving away from the periphery toward the center.