Prohibited and illegal

Can an object that is being prohibited be legal? Is this even a sentence that makes sense? In fact this bought me to more questions that i still cannot ans.

Prohibited
–verb (used with object) the action of a subject
1.to forbid (an action, activity, etc.) by authority or law: Smoking is prohibited here.
2.to forbid the action of (a person).
3.to prevent; hinder; preclude: Modesty prohibits me from saying what happened.

Illegal
–adjective
1.forbidden by law or statute. To modify a noun
2.contrary to or forbidden by official rules, regulations, etc.: The referee ruled that it was an illegal forward pass.
3.Unacceptable to or not performable by a computer: an illegal operation.

The word 'prohibited' has 3 meanings, of which 1 includes the prohibition due to the law and another the prohibition due to the action of. Similarly, illegal has 3 meanings of which 1 indicates that the noun is forbidden by law or forbidden by rules. Hence by not indicating what it is caused by, by law or by rule, the sentence can make sense.

However this sentence is weak as it is ambiguous and can cause confusion. A better way to phrase it would be "This is prohibited by the rules but legal in the eyes of law", or "This is made illegalised by the rules but made legalised in the eyes of law" or "This is prohibited by the rules but not prohibitive in the eyes of law.

Comparing "prohibited" and "made illegalised"
Comparing "made legalised" and "not prohibitive" and "legal"
One will then question what is the difference with (a) and (b)?

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Adjectiveillegalised (not comparable)

Positive
illegalised
Comparative
not comparable
Superlative
none (absolute)

-adjective
Made illegal.
After contentious protests, gambling was illegalised by the legislature.

–adjective
1.forbidden by law or statute.
2.contrary to or forbidden by official rules, regulations, etc.: The referee ruled that it was an illegal forward pass.