Some of the four basic elements of simile—the subject, comparator, marker, and respect—may be omitted, but different omissions can lead to different figures.
If both terms remain and the marker and respect are omitted, the structure may be an emphatic simile. If one expression is used for something else with a clue excluding literal reference, the question is one of metaphor or figurative usage.
“Zayd is a lion”: conventional emphatic simile with both terms.
“I saw a lion on the battlefield”: with context establishing a courageous person as intended, the use of “lion” raises the issue of metaphor.
The distinction prepares for the next section on literal and figurative usage.