having no depth; appearing shallow or superficial, or sometimes literally impossible to measure the depth of.
From 'depth' plus the suffix '-less' meaning without or lacking. This suffix (Old English origin) has been used for centuries to create adjectives meaning the absence of a quality.
The suffix '-less' is incredibly powerful in English—it lets us instantly describe what something is NOT, so 'depthless' tells us depth is completely absent, whether we're talking about a puddle or someone's shallow thinking!
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