identeco

Root plus suffix, and the root has no page here. Identeco is identa, identical, plus -ec-, the suffix that turns a quality into an abstract noun. Bona gives boneco, goodness. Libera gives libereco, freedom. Identa gives identeco, sameness. The honest note is that identa itself does not appear in this course's frequency list at all, so it has no word page: the derived abstract noun is commoner in real Esperanto than the adjective it is built from, which happens more often than you would expect.

The verb does have one. Identigi, rank 2503, is identa plus -ig-, to make identical, which in practice means to identify: to establish that this person and that name are the same. Between the two of them you can say most of what the family is for without ever needing the bare adjective.

Two senses, and English blurs them the same way. The first is logical sameness: the identity of two figures, two signatures, two accounts of the same night. The second is personal: who someone is, the thing a passport is supposed to prove and a large city is supposed to erode. Esperanto does not split these either, so context carries the whole load. An ID card is identeca karto or, more often written, identiga dokumento.