na-adjective
necessary and sufficient
Used in logic, mathematics, and formal contexts to describe conditions that are both required and enough. In everyday language, it can mean 'just right' or 'exactly what is needed'.
この条件は必要十分です。
This condition is necessary and sufficient.
必要十分な量の水を加えてください。
Please add a necessary and sufficient amount of water.
Compound of 必要 (necessary) and 十分 (sufficient). The exact historical derivation is uncertain, but it is a straightforward combination of two common Sino-Japanese words.