A person's first language; the language learned naturally in early childhood or at home.
私の母語は日本語なので、英語より日本語の方が表現しやすい。
My mother tongue is Japanese, so it's easier for me to express myself in Japanese than in English.
子どもは家庭での会話を通して母語を習得することが多い。
Children often acquire their mother tongue through conversations at home.
留学先では母語を使う機会が少なくなることもある。
When studying abroad, there are often fewer opportunities to use one's mother tongue.
In linguistics, a reconstructed ancestral language believed to be the common ancestor of a language family (protolanguage).
ラテン語はロマンス語の母語（祖語）の一例として研究されている。
Latin is studied as an example of a protolanguage (ancestor language) for the Romance languages.
比較言語学者は語彙対照から母語を復元しようとする。
Comparative linguists try to reconstruct protolanguages from vocabulary comparisons.