recondite

obscure, hidden, or difficult to understand

Roots

cond / condere: put away, store, hide, or preserve
re-: back, again, or backward motion

Other words with the cond / condere root

abscond: to run away secretly or hide away
condiment: a seasoning or sauce added to food

Recondite knowledge feels stored away in a hidden cabinet: hard to reach unless someone opens it.

The lecture became recondite when the professor stopped using examples.

Recondite keeps the hidden-away side of condere. The knowledge may exist, but it is tucked out of ordinary reach. That is why recondite writing feels obscure rather than merely hard.