necesario
/neθeˈsaɾjo/ · A2 · adj
necessary, requisite
necesario = necessary: swap English -ary for Spanish -ario
From Latin necessarius (unavoidable), the same root as English necessary. The -ary to -ario swap is a regular pattern: contrario, primario, salario. Spanish spells it with one s and c before e is /θ/ in Spain.