1A mimetic word describing the feeling of being irritated, annoyed, or on edge when things don't go one's way. Most often used verbally as イライラする; also functions as a noun and adverb. The kanji form 苛々 is rarely seen in modern writing — katakana イライラ is by far the most common form.
渋滞で全然進まなくて、イライラしてきた。
We're stuck in traffic and not moving at all — I'm starting to get irritated.
お腹が空くとついイライラしてしまう。
When I get hungry, I tend to get short-tempered.
そんなにイライラしないで、深呼吸して。
Don't get so worked up — take a deep breath.
最近仕事が忙しくて、イライラが溜まっている。
Work has been hectic lately and my frustration is piling up.
弟は宿題が分からなくて、イライラと机をたたいていた。
My little brother didn't understand his homework and was pounding on the desk in frustration.