The kanji 複 primarily conveys the idea of "duplicate," "multiple," "complex," or "double." It signifies something that exists in more than one instance, involves multiple parts, or is composed of different elements. This can range from physical duplication to more abstract concepts like a "complex" system. It often implies a repetition or a layering of things.

・On-yomi (音読み): フク (fuku) ・Kun-yomi (訓読み): None, or rarely used as a Kun-yomi.

⚫︎ 複数 Translation: multiple; several ⚫︎ 複合 Translation: composite; complex; combined ⚫︎ 重複 Translation: duplication; repetition; overlap

The correspondence with Vietnamese is that the kanji 複 has a high correspondence rate. ⚫︎ The Vietnamese word "phức" (or "phức tạp") derived from Sino-Vietnamese (漢越語) shares the same origin as the kanji 複.

The kanji 複 is a phono-semantic compound (形声文字 - keisei moji). It is composed of two parts: ・The phonetic component is 復 which provides the sound (fuku in Japanese). ・The semantic component is a component related to "many," or "double". The character thus combines a sound element and a semantic element to indicate meaning. It's essentially an extension or variation of the character 復 to specify the sense of "multiple" or "duplication."