enketo

Enketo covers two things English splits: the official investigation - a police inquiry, a judicial inquest, a formal look into what happened - and the survey, a methodical canvassing of what people did or think. The verb is enketi, the questionnaire is an enketilo, the professional who does it is an enketisto, and an opinion poll is an opinienketo.

What separates it from esplori is where the evidence comes from. Esplori is research in general, including the kind you do to rocks. Enketo leans on what the group under study says about itself, which is why the same word serves for interviewing witnesses and for asking a thousand people who they will vote for. Both methods have the same weakness and the same word admits it.

The seam that is not there. Enketo looks like en- plus a root ket-, and it is not. There is no root ket- in Esperanto; nothing is being gone "into". The word is enket-, one borrowed root from French enquête, and the en at the front is the French preposition that fused to the Latin verb fifteen centuries before Esperanto existed. Etymology and word-building are different questions: the history really does contain an "in", and the modern grammar does not.