na-adjective, noun which may take the genitive case particle 'no', noun
deepest
Used as a noun or adjectival noun to describe the greatest depth, often in geographical, emotional, or abstract contexts.
The deepest part of this lake is about 100 meters.
His words resonated in the deepest part of my heart.
Compound of 最 (sai, 'most') and 深 (shin, 'deep').