An attention-grabbing particle meaning 'behold!' or 'look!'—though grammarians debate whether it's truly an imperative or an adverb. It appears with nouns ('behold, a virgin'), pronouns ('behold, I stand at the door'), and verbs in any tense ('behold, he comes'). The New Testament uses it liberally, especially in narrative and apocalyptic literature. Angels announce with ἰδού, Jesus teaches with it, and Revelation punctuates visions with it. The particle even works with verbs of hearing ('Listen! I hear a sound'). Functionally it frames what follows as significant, surprising, or requiring notice.