expression
in other words; to put it another way; if we rephrase it
Used to introduce a restatement or clarification of what was just said. Functions as a conjunction-like phrase.
言い替えるなら、それは不可能だということです。
In other words, it means that it's impossible.
彼の説明はわかりにくかった。言い替えるなら、要点がはっきりしなかった。
His explanation was hard to understand. To put it another way, the main point wasn't clear.
つまり is a more common and casual way to say 'in other words' or 'that is to say'. 言い替えるなら is slightly more formal and explicitly means 'if we rephrase it'.
換言すれば is a more formal, written-style equivalent, often used in academic or technical contexts.
From 言い替える (to rephrase, to say in other words) + conditional なら (if).