One of the most difficult things about learning another language can be finding an easy way to express ideas that seem simple in your mother tongue. It can be frustrating to learn that there isn’t a one-to-one ratio for every English adjective and verb.
One of the parts of Japanese that seems especially complicated is the four-character compound (四字熟語、よじじゅくご). This is because they are often idiomatic (一石二鳥、いっせきにちょう), and many idioms don’t translate as neatly as those poor dead birds.
I just learned one recently that’s very easy to remember and expresses what seems like a comparatively simple concept in English. 疑心暗鬼（ぎしんあんき）means paranoid. It’s often used like an adjective (彼は疑心暗鬼だ。) or in combination with ～になる（疑心暗鬼になる。）.
Here’s the character by character breakdown:
疑 – suspicious, doubtful
心 – heart
暗 – dark
鬼 – monster
It isn’t the official way to say paranoia (which is 被害妄想、ひがいもうそう), so it can also be translated as “suspicious,” “wary,” or “fearful,” but it’s by far the coolest way to express this idea.
Kenkyusha’s New Japanese-English Dictionary (“The Green Goddess”) provides a most excellent translation – “Fear peoples the darkness with monsters.”