زيد كالأسد في الشجاعة
Zayd is like a lion in courage.
Zayd is the subject of comparison, the lion its standard, kāf the comparison marker, and courage the shared quality. Omitting “in courage” makes the shared quality implicit. Omitting the marker as well and saying “Zayd is a lion” can produce a concentrated simile, provided the comparison's two sides remain grammatically identifiable.
ConstructionRhetorical effect
زيد كالأسد في الشجاعةBoth marker and point of likeness are expressed
زيد كالأسدThe point of likeness is inferred
زيد أسدThe marker is suppressed, strengthening the identification
This is a comparison of grammatical constructions; “lion” is not automatically a metaphor in every such sentence.