"At dark" is a phrase commonly used to indicate the time of day when the sun has set and the sky has turned dark. Some other synonyms for this phrase include "in the evening," "at nightfall," "after sunset," "in the twilight," "in the gloaming," and "under cover of darkness." These phrases could be used interchangeably depending on context and personal preference. Whether it's for writing a book, setting the scene in a movie, or simply describing an event that occurred after sunset, these synonyms provide a range of options to add variety to your writing and conversation.