naiva

Naiva carries the French range as well as the English one. It can mean gullible, easily taken in, the way English usually means it; it can also mean artless in a good way, the unspoilt directness of a child or a folk painting. Context decides, and naiva arto is a compliment.

The apparent seam is a mirage. Esperanto does have an -iv- suffix, unofficial and technical, the one in kreiva and produktiva (see the unofficial affixes), but naiva is not built with it and will not divide into nai- plus anything: naiv- is one root, borrowed entire. The same warning covers every other international adjective shaped like it, aktiva, pozitiva, relativa and the rest. Where there is a real connection is further back: the Latin nasci behind naiva is the same verb behind naskiĝi, so the far cousin of "naive" is "to be born". That is history, not word-building, and it will not help you build a new word.