Certain tools and substances (some fertilizers, nuclear technology, among others) can have both a legal peaceful application, or an illegal destructive use. What's the word for describing this type of ambiguous stuff?
This might get a better answer in law.SE, but in english.SE it has a chance too. Here people seem more open towards single word requests.
It sounds like they might be termed controlled tools and substances (as with drugs). Legal is obvious. Illegal is obvious. I found an online article discriminating illegal vs. controlled substances (drugs). Another term, regulated, might also be applicable.
I hope these descriptive terms are what you are looking for: "controlled or regulated".
I don't know of a single word for this. The common term is dual-use:
In politics and diplomacy, dual-use is technology that can be used for both peaceful and military aims.
More generally speaking, dual-use can also refer to any technology which can satisfy more than one goal at any given time. Thus, expensive technologies which would otherwise only benefit civilian commercial interests can also be used to serve military purposes when not otherwise engaged such as the Global Positioning System.
In addition to the words suggested by others, another possibility is restricted.
Contracts for the import or export of restricted technology must be approved and licensed, whereas such contracts for free technology need only be registered. (source)
The medical or nurse practitioner or eligible midwife may verbally authorise the administration of a restricted substance. (source)
The answer depends on whether you are focussing on legality or on the fact that there are beneficial and harmful uses. If your concern is legality then the answers giving 'controlled' or 'regulated' are to the point. Control and regulation are the response of the authorities to the co-existence in one substance of good and bad uses.
But there are such substances that the authorities have not got around to controlling (yet). If you want a single word for that why not say 'dangerous'? Very few things are 100 per cent dangerous. Dangerous things can serve useful purposes.
Sanctioned (or some form of "sanction") maybe? Can refer to a use that is "approved by" some official body, or as a penalty for having used it.
This phrase implies that it is more illegal than legal, but "substantial non-infringing use" from the far-famed Sony v. Universal federal (United States) court case comes to mind. I do not know if this is useful to you.
Wikipedia on the case: https://en.wikipedia.org/wiki/Sony_Corp._of_America_v._Universal_City_Studios,_Inc.
