كالراقم على الماء
Like someone writing upon water.
When fruitless work is likened to writing on water, the comparison term is not merely “a writer.” The restriction “on water” is essential because it makes the effort transient and ineffective. Replacing water with a durable tablet could change the point of the image entirely.
This is a qualified single term: fundamentally a single person or agent considered under a relevant activity and circumstance. The number of words in the description does not by itself make it a composite configuration.