inteligenteco

Inteligenteco is a genuine build and a clean one: inteligenta, the adjective, plus -ec-, the suffix that turns a quality into a thing you can talk about. Intelligent -> intelligent-ness.

-Ec- is one of the workhorses of the language and it costs nothing to learn, because it takes any adjective at all: bona -> boneco (goodness), libera -> libereco (freedom), varma -> varmeco (warmth), homa -> homeco (humanity, the quality). English needs -ness, -ity, -dom, -hood and -th for the same job and cannot tell you which one a given adjective takes. Esperanto has one answer and it is always right.

Do not confuse it with -aĵ-, which makes a concrete thing rather than a quality: boneco is goodness, bonaĵo is a good deed. The test is whether you could point at it.

One sense only. English "intelligence" also means gathered secret information - military intelligence, an intelligence service. Inteligenteco does not carry that at all. The spying sense is sekreta informado or spiona servo. Keep inteligenteco for the quality in somebody's head.