The difference between Simple and Unchallenging

When used as adjectives, simple means uncomplicated, whereas unchallenging means not challenging.

Simple is also noun with the meaning: a herbal preparation made from one plant, as opposed to something made from more than one plant.

Simple is also verb with the meaning: to gather simples, i.e., medicinal herbs.

check bellow for the other definitions of Simple and Unchallenging

Simple as an adjective:

Uncomplicated; taken by itself, with nothing added.
Simple as an adjective:

Without ornamentation; plain.
Simple as an adjective:

Free from duplicity; guileless, innocent, straightforward.
Simple as an adjective:

Undistinguished in social condition; of no special rank.
Simple as an adjective (now, rare):

Trivial; insignificant.
Simple as an adjective (now, colloquial):

Feeble-minded; foolish.
Simple as an adjective (technical):

Structurally uncomplicated. Consisting of one single substance; uncompounded. Of a group: having no normal subgroup. Not compound, but possibly lobed. Using steam only once in its cylinders, in contrast to a compound engine, where steam is used more than once in high-pressure and low-pressure cylinders. Consisting of a single individual or zooid; not compound. Homogenous.

Examples:

"a simple ascidian"
Simple as an adjective (obsolete):

Mere; not other than; being only.

Simple as a noun (medicine):

A herbal preparation made from one plant, as opposed to something made from more than one plant.
Simple as a noun (obsolete):

A term for a physician, derived from the medicinal term above.
Simple as a noun (logic):

A simple or atomic proposition.
Simple as a noun (obsolete):

Something not mixed or compounded.
Simple as a noun (weaving):

A drawloom.
Simple as a noun (weaving):

Part of the apparatus for raising the heddles of a drawloom.
Simple as a noun (Roman Catholic):

A feast which is not a double or a semidouble.

Simple as a verb (transitive, intransitive, archaic):

To gather simples, i.e., medicinal herbs.