noun
A word formed by combining two or more independent words or stems, such as 合成語 itself (合成 + 語).
「合成語」は、二つ以上の単語が組み合わさってできた語です。
A 'compound word' is a word made by combining two or more words.
From 合成 (ごうせい, 'synthesis, composition') + 語 (ご, 'word').