I'd like to ask if we can use the word initiative as an adjective. I have found it used that way, but there is no entry for initiative as an adjective in the Oxford Advanced Learners' Dictionary.
Actually initiative as an adjective can be found in dictionaries as shown below. I'd say that is not a common adjective and initiatory, introductory or initial are valid alternatives.
- Of or relating to initiation.
Used to initiate; initiatory.
of or concerning initiation or serving to initiate; initiatory.
initiative - serving to set in motion;
"the initiative phase in the negotiations"; "an initiatory step toward a treaty";
Compressed dry guncotton is easily detonated by an initiative detonator such as mercuric fulminate.
In 1908 an act was passed providing for local option in regard to the sale of intoxicating liquors, by an election to be called an initiative petition, signed by at least 35% of the electors of a county.
The first attempts to utilize the explosive power of nitroglycerin were made by Nobel in 1863; they were only partially successful until the plan, first applied by General Pictot in 1854, of developing the force of gunpowder in the most rapid manner and to the maximum extent, through initiative detonation, was applied by Nobel to nitroglycerin.
Is "turkey" an adjective? I found it used that way. As in "turkey dinner". No, it's a noun adjunct, in the same way as Janus said in one of the comments.
A noun adjunct is (wikipedia)
an optional noun that modifies another noun; a noun functioning as an adjective
Is "chicken" and adjective? That's a bit more complicated. There's "chicken dinner" and "chicken soup". In these cases, it's a noun adjunct.
"Chicken" is complicated by being identified with "cowardly" (an adjective), as in "The man is chicken". "Chicken" is accepted as an adjective here. What about "Jack is the chicken man"? I would stick with noun adjunct, even if the meaning can only be determined by context. (Is Jack cowardly or is Jack the man that sells chickens, or is he something else?)
This brings us to your specific question about "initiative". This is commonly identified as a noun and not as an adjective.
Using some examples provided from another answer (there was no context to refer to in the original question), I'll provide some thoughts and then make my point.
"the initiative phase in in the negotiations"; "an initiatory step toward a treaty";
Both cases look like clumsy efforts to say initial (in the first cue) and initiating or initial in the second case.
...detonated by an initiative detonator ...
A better word choice would be initiating
...by an election to be called an initiative petition...
This is literally referring the the procedure (noun) that enables a number of voters to propose a law by petition, which is called an initiative, which is a noun. This is a case of being a noun adjunct.
...developing the force of gunpowder in the most rapid manner and to the maximum extent, through initiative detonation, was applied by Nobel to nitroglycerin.
A better choice might be an initiating
As these examples show, It's easy to mentally identify a noun that has been used as a noun adjunct as an adjective. But when you to this, you may begin put the word into tortured positions (as adjectives) that make you stare and wonder if they are really right. You'll check a dictionary and ask some experts. You'll get advice that contradicts your common sense. It might be easier, now that you are aware of the existence of noun adjuncts, to say to yourself "there is probably a better way to say this".