|Kanji in this term|
From Old Japanese. Derived as the transitive/causative counterpart to intransitive verb 至る (itaru, “to come; to go; to reach a point in time or space; to result in”), originally meaning the same as causative conjugation 至らせる (itaraseru, “to make something or someone come or go; to make something reach a point in time or space; to cause a certain result”).
Alternative forms 
- In modern Japanese, this word is generally written in hiragana, with the kanji spelling used in more formal writing.
Usage notes 
When speaking in formal situations, いたす is used in place of する by the speaker in deference to the listener. This is part of the subset of Japanese formal language (敬語 (けいご, keigo)) referred to as "humble" language (謙譲語 (けんじょうご, kenjōgo)). This word has also found its way into certain common expressions, such as どういたしまして (dō itashimashite, “it's all right; you're welcome”).