Used to summarize or give a concise conclusion about something.
In a word, he is a very kind person.
To put it briefly, this movie was moving.
Standard kanji-kana mixed spelling.
Variant with いう in kana; slightly less formal.
Phrase composed of 一言 (ひとこと, 'a single word') + で (particle) + 言う (いう, 'to say') + と (conditional particle). Literally 'if one says it in one word'.