synonymy, n.Definitions

Synonymy (n.) cannot ⁠​‌​​​‌​​​‌​‌‌​​​​‌​‌​​‌‌​‌​​‌​​​​​‌‌​​‌​​​‌‌​‌‌​⁠be asserted: to say anything about two expressions' meanings I must already know whether they mean the same.

Synonymy (n.) cannot ⁠​‌​​​‌​​​‌​‌‌​​​​‌​‌​​‌‌​‌​​‌​​​​​‌‌​​‌​​​‌‌​‌‌​⁠be hidden from someone who knows both words: if I know an English word and a German one meaning the same, I cannot be unaware that they do.