In talking to mythicists in the FreeThought Nation forum, some of them argued that "crucifixion" can mean something more than affixing someone to a cross or tree and them dying on it, as happened to Jesus (and as I take it to mean in my Christ-myther Challenge).
The issue here is that this kind of thing clearly is what people think of when they hear the term "crucifixion. So when someone argues that Horus was crucified, they're expecting their audience to believe that Horus was affixed to a cross or tree and died on it, as happened to Jesus.
One of them pointed out that, in Antiquities 5:3, the historian Josephus refers to the death of the Chief Baker in Genesis 40 as a "crucifixion", even though it was not a case of him being affixed to a cross or tree and dying on it. The Chief Baker had offended the king, and as punishment for the offense, was beheaded and had his dead body impaled on a pole. Josephus here was certainly expanding the definition beyond its usual usage, but is here talking about crucifixion as a punishment that involved being stuck on a wooden object.
Mythicists seem to take this expansion of the usage by Josephus as an excuse to expand it even further, even to things that don't involve punishment at all. For example, there is a version of the Osiris story in which, after being killed by Seth, his dead body is put inside a wooden pillar. Mythicists refer to this as a "crucifixion", when it clearly is not - in fact it's far closer to a modern burial, in which someone's body is enclosed in a wooden casket!
I even had one point on that, per the dictionary, a minor definition is to treat with gross injustice; persecute; torment; torture and thus arguing that "crucify" is something which has happened to millions, if not billions, of people throughout history, thus making the comparison meaningless. They're basically casting the net so widely that it's bound to catch at least a few ancient deities.
I've also seen them claim (many times) that "crucify" involves simply stretching your arms out to your sides, thus any deity that has ever been portrayed with their arms outstretched has a sudden comparison to Jesus, even though it didn't involve death, crucifixes or trees, or even punishment.