"A friend of long standing" is how "crony" is defined; and it comes from the Greek for "time", namely "chronos", which is also at the root of your clock - or chronometer, should you be afloat. When its use began it meant simply that; a pal, perhaps from student days. More recently it's acquired a sinister overtone, suggestive of improper relationships between people whose advertised interests are at arms' length; people in power, for example, hobnobbing with others whom they are supposed to control... in the public interest, of course.
Government and business, for example; or as Sanders usually abbreviates it, "Wall Street". He thinks big business is in bed with slimy politicians, and he's not far wrong. He thinks Hillary would be one such, and he's right.
The word set me wondering about how eager business owners may be to influence government, and I can perceive three different kinds - with three degrees of guilt.
First, there is the reluctant crony. He might own a one- or two-person business, but he's forced (at gunpoint, ultimately) to pay government some money and subject himself to its rules - even to get a "business license" as if earning a living by honest trade were something for which permission is needed. As a condition of survival he must fill out its paperwork and be polite to its snoops and bureaucrats, but beneath it all he hates their guts and wishes they did not exist. If he's not already an anarchist, he certainly should be.
Then comes the active crony, perhaps running a larger business and who realistically recognizes that it's impossible (short term) to beat them, so he might as well join them; not merely cooperating but entertaining some of the power-wielders so as to gain their favors. Those favors would include the swift granting of permits and the repeal of particularly obstructive laws (so that he can prosper better, create more jobs for voters, and contribute more generously to re-election funds...) to the enactment of new laws that would hurt his rivals more than they would hurt him. That trick is often pulled by bigger firms, who wish to keep more nimble competitors from taking more of "their" market. So active cronies scratch each others' backs, working posiitvely for each others' benefit. These are much more detestable than the first kind.
Lastly there is the contractor crony. These are businesses who supply goods or services to government, and often to government alone, sometimes in a very complex manner. Any firm that accepts orders from any government is in this category - for example, a paving contractor. He may well have other customers (with driveways to be paved) but the best orders come from cities and states with miles of roadways to lay and maintain.
A key member of the "contractor" class is, I'd say, anyone in banking. In concept that need not be so, but financial regulations are so pervasive that to keep succeeding a banker really "has" to move from the "active" to the "contractor" class of crony, and actually service the state. He does it mainly through his trade association, the Federal Reserve, chartered by government; it gladly fabricates trucks of money for the Treasury upon demand, in return for the favor that makes members free to lend out nine tenths of it at interest, when the freshly minted currency circulates. That's called "fractional reserve banking"; it is deeply kriminal but is the mainspring both of inflation and of banker profitability.
The ultimate "contractor" crony is our old friend the MIC, and is the most loathsome of all. The government crony is the military and all who govern it, and the business crony is the manufacturer of weapons for them to buy - and use, to kill and maim their enemies. Often the government is the firm's only customer, unless a permit is granted to export some weapon to an ally who can be relied upon to make war alongside Uncle. The borderline between supplier and customer in this Military Industrial Complex is fuzzy. On the QuitGov site, employees of suppliers of this category are particularly encouraged to quit their jobs.
Weapon makers depend heavily on repeat government business, so must also encourage the election of candidates likely to wage war; for replacement orders can come only from obsolescence (a long wait) or from use and destruction (much quicker.) So MIC firms have ample reason to want a warmonger in the White House, and they have done very well for many decades. On the (R) side of the ruling duopoly, Trump appears to have thrown a monkeywrench into that, as this excellent AntiWar article explains, but on the (D) side no such impediment is yet set to slow down Hillary.
Trump, incidentally, looks to me like a Reluctant or perhaps an Active cronyist. He builds tall buildings in New York, so it's impossible not to cosy up to the tin political gods there, and he did the world a service when he openly admitted that when one of them asks for a donation, he pays up... in expectation of a favor. He also became the nemesis of Rand Paul, when the latter began to criticize those generous donations, and he responded that Paul had seemed happy enough to receive one of them!
Sanders, likely at this writing not to be a finalist, seems to have grasped the evil of cronyism of the third kind, but not the underlying necessity of the first or even the second sort above, nor that all of them are brought about entirely by the existence of government. When that has evaporated and a zero government society begins, there will be no cronies in it to wield any power, so those on the business side of the bed will suddenly find themselves crony-less and most of them (though not the bankers or MIC folk) will be delighted.
But hey, if Bernie had understood that, he'd be a libertarian and doubtless running as such.