Short of getting a Cosmic Cube/the UN/the IG Thanos' only shot is to trick Q into giving up his powers.
Q is just too powerful for Thanos. Death doesn't even exist for the Q IIRC, they have to be depowered and turned human before they can be killed. And only another Q or a similarly powerful/more powerful being can accomplish that.
__________________
“Where the longleaf pines are whispering
to him who loved them so.
Where the faint murmurs now dwindling
echo o’er tide and shore."
-A Grave Epitaph in Santa Rosa County, Florida; I wish I could remember the man's name.
Q displayed the ability to wipe out entire races by thinking about it. Sciatic in multiple points of time.
Basically classic skyfather level type stuff
__________________ Quotes from Hia8:
"I claimed that the science is sometimes faulty."
"You don't understand. This is fiction. That means none of this stuff really happened."
"There is no writer to purposely ignore a character's natural ability just because it suits the story."
"in some cases because the writer knows that Character A will dominate Character B easily and refuses to allow this to happen for the sake of the story."
That was a Douwd from the episode called "The Survivors". He killed every member of a species no matter where they were in the univserse by a single thought because one of them killed his human wife.
I don't think he was as powerful as a Q. Q would have resurrected his wife which he couldn't do.
And Q's restrained by an equivilent of the Prime Directive. He's never killed anyone directly, although indirectly caused some deaths, and that was only for instructional purposes, as all life in Federation territories was threatened by The Borg...
Sisko knocked Q on his ass. What did Q do about it?
Nothing. Didn't even bother toying with him like he does Picard, he simply stopped dealing with him.
Are you trying to say that Sisko is greater than Q? Really?
Anyways, Q is bound by certain rules, but just so happens to break them all the time regardless. He doesn't kill because he really isn't that much of a douche.
You can't compare Star Trek and Marvel directly, since Star Trek doesn't have abstracts. We do know, however, that Q can resurrect the dead (and kill, of course).
The Q, in Star Trek, are the closest thing to omnipotents (Q states himself to be omnipotent, but we know this isn't quite true). For example: they can be depowered by other Q, there are multiple Q, and the series finale of TNG showed that Q's interest in humanity was due to humanity's potential to surpass the Q in the distant future.
Regardless, Q is far and away above Thanos in power. Even if he couldn't kill him, he could always just incapacitate him for eternity or some other equivalent victory.
__________________
"And then there was nothing. A once broken something now void.
And on the first day, Doom spoke... 'Be.'
And then there was life."
This is all somewhat retconned in Voyager, where the Q civil war shows Q's offing each other left and right with what appear to be normal firearms, but was actually Q super weapons. If Thanos got his hands on one of those suckers...
It was stated in Voyager that their fight was far beyond what we could perceive, and so we interpreted it as a Revolutionary War/Civil War era fight with rifles/muskets and the like. They weren't actually using guns, or even weapons of any kind. Was all their own power.
It's basically the same as Galactus in that way.
__________________
"And then there was nothing. A once broken something now void.
And on the first day, Doom spoke... 'Be.'
And then there was life."