Just as you have used various English suffixes to turn nouns into adjectives ("-ly", "-ish", "-ful", ...), there are a number of ways to do this in Japanese, too. Most important ones are:
損 (disadvantage) / 損な (disadvantageous)
不思議 (mystery, wonder) / 不思議な (mysterious)
真 (truth) / 真の (true)
永遠 (eternity) / 永遠の (eternal)
子供 (child) / 子供っぽい (...