What literary term, represented by an image or idea in a text, consists of five letters with "i" as the fourth letter?

The literary term you're describing that is represented by an image or idea in a text, consisting of five letters with "i" as the fourth letter, is "motif." A motif is a recurring element in a piece of literature that has symbolic significance and contributes to the development of a theme.

Extra: A motif can be almost anything: a sound, an expression, a color, an object, etc. It differs from a theme in that it is a concrete manifestation of a text's underlying themes, rather than an abstract concept. For instance, if you read a book in which birds are mentioned frequently and seem to play a significant role in the story, the birds could be considered a motif, potentially symbolizing freedom. The repetition of a motif can help to reinforce the themes and ideas of the work in the reader’s mind. It's a tool that writers use to subtly guide a reader's interpretation of the text or to create cohesion within a work. Different motifs contribute to building layers of meaning and complexity in literature, and identifying them helps in understanding the author's message and the text's deeper significance.