のみならず is a structure consisting of のみ, the literary particle equivalent of だけ meaning ‘just’ or ‘only’, the negative stem-form of the う-Verb なる ‘to be’, and the literary auxiliary verb ず, which connects with verbs in the same way, and carries the same meaning as ない. This expression indicates that something is ‘not just (A), but also (B)’, or ‘not only (A), but (B) too’.
のみ connects to words in the same way as だけ, so this pattern will be seen following Verbs, い-Adjectives, な-Adjectives, or nouns.

• 今日（きょう）は仕事（しごと）に遅刻（ちこく）したのみならず、帰（かえ）りの終電（しゅうでん）も逃（のが）してしまった。
  Today I was not only late for work, but also missed the last train home.
• 日本（にほん）の夏（なつ）は暑（あつ）いのみならず湿気（しっけ）が高（たか）いから熱中症（ねっちゅうしょう）になりやすい。
  Japanese summers are not only hot, but also humid, making it easy to suffer heat stroke.
• あのパソコンは便利（べんり）のみならず、安（やす）いので他（ほか）のと比（くら）べてたくさん売（う）れています。
  That computer is not only convenient but also inexpensive, so it sells a lot more compared to the others.
• この漫画（まんが）は子供（こども）のみならず大人（おのた）の間（あいだ）でも人気（にんき）があります。
  This manga is popular not only among children but also among adults.

Occasionally, のみならず may function as a conjunction, appearing at the beginning of a new sentence. In these cases, the meaning is the same, but usually translates closer to ‘what’s more’, ‘furthermore’, or ‘moreover’.

• 田中（たなか）さんは私（わたし）の先輩（せんぱい）だ。のみならず、命（いのち）の恩人（おんじん）でもある。
  Tanaka-san is my senpai. Furthermore, he is the person that saved my life.
• 高橋（たかはし）さんはサッカーの専門家（せんもんか）だ。のみならず野球（やきゅう）にも詳（くわ）しい。
  Takahashi-san is an expert on soccer. Moreover, he is also very knowledgeable about baseball.