زَيْدٌ كَالْأَسَدِ
Zayd is like a lion.
The prefixed «كَـ» explicitly marks the intention to compare Zayd with the lion in some respect. Commonly the intended quality is courage, but a different contextual setting might suggest another feature. The particle itself does not name the precise point of resemblance.
Grammatical analysis: «زَيْدٌ» is the subject of the nominal sentence; «كَالْأَسَدِ» functions in the predicate structure. The kāf is a preposition marking resemblance and «الْأَسَدِ» is in the genitive after it. The example helps identify the comparison marker and each of the two terms while keeping the intended point distinct.