noun, noun which may take the genitive case particle 'no'
Describes something that exists or occurs without human intervention, or a quality that is inherent and unforced. Often used as a no-adjective.
This park retains scenery that is completely natural.
naturally; spontaneously; of its own accord
Used adverbially to describe something happening without external force or artificial effort, often with に or as an adverbial noun.
彼の笑顔には天然自然の優しさがある。
His smile has an innate gentleness.
The problem resolved itself naturally.
Children learn language spontaneously.
天然 means 'natural' as opposed to artificial, often used for natural resources or innate qualities. 天然自然 doubles the idea for emphasis and is more formal.
A yojijukugo combining 天然 (natural, innate) and 自然 (nature, spontaneous), reinforcing the idea of something being completely natural and unforced.