dentro
inside
de-
of, from
+
enter
to go inside
Dentro means inside. Think of it as de-0 (of, from0) + enter1 (to go inside1), as if you're coming from the act of entering.
adverb
- insideIn or to the interior of something; insideEl gato está dentro de la caja. // The cat is inside the box.
- withinWithin a specified period of timeLlegaré dentro de una hora. // I'll arrive within an hour.