1. thin (air), weak (liquid), dilute, sparse (population), rarefied

noun (common) (futsuumeishi) adjectival nouns or quasi-adjectives (keiyodoshi)

2. lacking (enthusiasm, consideration, substance, etc.), insubstantial, deficient, tenuous (link)

noun (common) (futsuumeishi) adjectival nouns or quasi-adjectives (keiyodoshi)