This is the 840th most frequent German word.
tiefer
"Deeper"
In this sentence, 'tiefer' is used as a comparative adjective to describe the depth of the lake, comparing it at this location to other locations.
Der See ist hier tiefer als an anderen Stellen.
The lake is deeper here than in other places.
Here, 'tiefer' is used as an adverb to describe the degree or extent of the relaxation he is attempting to achieve.
Er atmete tief ein und versuchte, sich tiefer zu entspannen.
He took a deep breath and tried to relax more deeply.
In this sentence, 'tieferes' operates as an adjective in the comparative form, modifying 'Verständnis' (understanding) to indicate a greater degree or depth.