Hybrid computation combines discrete and continuous dynamics in the form of an entangled mixture inherently present both in natural phenomena, and in applications ranging from control theory to microbiology. The emergent behaviours bear signs of both computational and physical processes, and thus present difficulties not only for analysis, but also for describing them adequately in a structural, well-founded way. We present a while-language for deterministic hybrid computation HybCore and equip it with an operational and computationally adequate denotational semantics over a hybrid monad. As an intermediate step we develop a more lightweight duration semantics drawing on a duration monad that we introduce as a lightweight counterpart to the hybrid monad.