noun, na-adjective
plain and simple; naive; unsophisticated
Describes a person, idea, or thing that is straightforward and uncomplicated, sometimes with a nuance of being overly simple or lacking sophistication. Can be used both positively (unpretentious) and negatively (naive).
彼の考え方は単純素朴で、すぐに騙されてしまう。
His way of thinking is plain and simple, so he gets deceived easily.
この絵本は単純素朴な話だが、心に残る。
This picture book has a plain and simple story, but it stays with you.
Compound of 単純 (simple) and 素朴 (naive/unsophisticated). The exact historical derivation is uncertain, but the word is a straightforward combination of its components.