Looking at the lists, I'm seeing some of the Wall spells that require the Barrier word. While that makes complete sense from the normal standpoint, I was a bit confused. The spell level of, for example, Stone Wall word is level 5, which makes sense as the Wall of Stone spell was also 5th level, albeit a little stronger.
However, casting a spell as a barrier spell increases the level by 3, so would this make it cost an 8th level spell to be able to create said wall? I would not believe so, but I need something to verify that this is true or not.
Level: This line lists the minimum level for a wordspell containing this target word.
Basically, the level of the Target Word doesn't factor into the level of the spell. It can only be used in a spell that is of the appropriate level or higher though.
So basically, the Barrier word can only be used in wordspells of level 3 or higher, but won't increase the level cost at all.
I think you use the highest level word or the highest level effect word, not the sum of all the words.
In that regard, it's not the highest level word, but a mixture of the levels of the Effect words (which may or may not be altered through Meta words, or some other things).
For example, a level 7 wordspell can be made in a couple ways:
7
5/5 or 6/4
4/4/4 or 5/3/3
But these are only based on the Effect words. The Target word used shouldn't matter to this (provided the Target word's level is 7 or less), unless it is boosted and the boost specifically increases the Effect words (Selected does this, but most others only raise the level of the Target word, raising the minimum level of the spell they're placed in).
Meta words also tend to raise the level of Effect words in a spell, though not always, and Boosts available on some Effect words raise themselves up a bit.
...I think that's how all of these play out anyway. No guarantees.
A target word can only affect the level of the Wordspell if the target word has a higher requirement than the combination of the effect words. All 3 examples below use the lower tier Boost on the Burst Target Word.
Ex: Boost Burst (3) Frost Fingers (2) has a level 3 Target Word, but only a level 2 Effect Word. As such, the Wordspell is level 3.
Ex: Boost Burst (3) Winter's Wrath (8) has a level 3 Target Word, but is using a level 8 Effect Word. This Wordspell is level 8.
Ex: Boost Burst (3) Frost Fingers (2) Discordant Note (2) has a 3rd level Target Word, but the combination of Effect Words makes this a 4th level Effect, so this is a level 4 Wordspell.