The Spanish for “night”, noche, is related (via the common Latin ancestor) nocturnal.
Here’s the interesting part: the Latin sound “ct” consistently changed to the “ch” sound in Spanish. Think “lactose” and “leche”, or “octagon” and “ocho”. And this is another example of that pattern: the “ct” in “nocturnal” is the same as the “ch” in “noche”!