إن كان اللفظ متعددا والمعنى واحدا يسمى مرادفا
If the expressions are multiple but the meaning is one, they are called synonymous (mutarādif).
“Al-asad” and “al-layth” both denote a lion, and so illustrate synonymy in this respect.
Synonymy: different expressions with the same intended meaning.
Homonymy: one expression with distinct independent meanings.
These are converse patterns. Sharing a general topic is not enough for synonymy; the intended sense must coincide. Possible nuances of usage are a further question.