The magic seems to have an independent emotional mechanism at work, where the words are merely a guide to how to trigger that mechanism. That is, it isn't the physical sounds of the spell words, but rather the emotions and thoughts attached to the sounds (note that Dumbeldore can cast spells without speaking!). Hence, it would be the emotions in the situation that mattered, and would have to be discovered by experimentation! Particular definitions or interpretations of the words don't matter, as the words aren't the magic, but rather it is the feelings and the thoughts that trigger the magical manifestation.
In support of this view, from DVK, above:
"Lily's protection magic was triggered by her choosing to die to protect Harry and Voldemort giving her a choice." and Harry: “I meant to let him kill me!”
“And that,” said Dumbledore, “will, I think, have made all the difference.”
and a followup answer:
"Another example is the Cruciatus curse, as described by Bellatrix Lestrange :'You need to really want to cause pain... to enjoy it... righteous anger won't hurt me for long...' "
These support the notion that the magic itself is something whose substance is the emotions of the people involved. For example the books describe students saying the proper words and doing the proper motions, but the magic doesn't work. Hence, the magic has an independent mechanism that is outside of the actual words used and the actions that trigger it.
Given that, we can't rely upon the wording of the spell, but rather must discover, by experimentation, what emotional mechanism exists independently from the exact wording. The words provide the clues, but as the students discover while learning, the caster has to fiddle around until they discover the right emotions plus actions that actually work.
In a nutshell, the spell caster has to experiment to find the underlying emotional mechanisms behind the words of the spell.
So, let's apply that understanding to the rest of the arguments, such as from Oak:
"Pettigrew only said that the blood must be taken by force, the usage of the blood wasn't tied in, per say. Imagine if not only Voldemort, but also Draco needed the potion. In this hypothetical case, let's say that the potion would save their lives rather than create a new body. Draco sees himself as Harry's enemy for most of the books, but Harry would willingly give blood to save Draco. Let's say the same vial of blood is used in both potions that were used to save Voldy and Draco. Both were willingly given, even though only one was truly meant, but they'd both work, right? – Oak"
Applying the above understanding to this hypothetical, we'd have to fiddle around, to find out what works in the "real" world. We can't debate the wording of the spell plus actions taken! Trying to use dictionary definitions and introduce alternative interpretations of the spell words just makes the spell caster less likely to succeed in triggering the magic! The spell words can be given many different interpretations.. but those have no bearing.. it's the underlying emotions that result in the magic manifesting.
My guess is that the potion required the feeling of power of forcefully taking your enemy's blood. That dominant triumphant feeling of power. Making them helpless and taking their life's blood by the power of your own force. In that case, the potion would be person specific. It was created on behalf of Voldemort, at his will, manifesting his domination of Harry, his power over Harry. So, the potion would have no effect if used on Malfoy. We can't create a hypothetical spell to make a point, because it's the underlying real world mechanism that manifests! A spell based on forceful taking of blood seems that it would rely on that dominance feeling and so would be person specific, and the potion couldn't be used to save two different people, only the one person it was created specifically for.
"Let's put it this way - if you and I met in a dark alleyway, and you didn't like the look of me and cried out (without me doing anything), "Don't hurt me! Here, take my money!" and then I whacked you over the head, knocked you unconscious and took it anyway, I think most people would agree that I took it forcibly from you."
This argument seems to follow the emotion underlying the words of the spell. By whacking and taking, you gain the feeling of complete power over your victim, taking what you want from them.
If this is, indeed, the underlying mechanism of the spell, then it is the circumstance of Harry being made completely helpless and powerless, and the feeling of the Death Eaters taking Harry's blood at the will of Voldemort directing them. That feeling is what triggers the mechanism of the spell. Harry can offer, and be willing, and plead, and do whatever else he wants, but taking away all Harry's power, and Voldemort feeling his mastery as he extracts Harry's blood according to Voldemort's own will is what makes the spell work.