"boosted" vs. "additional"
This one players learn about very early on but it still bears repeating. A roll can never be "boosted" more than once. If two effects grant a "boosted" roll, you still only roll 1 extra die. If, however, something grants an "additional die", there's no such restriction. If pButcher charges a model on his feat turn, he's rolling 5 dice worth of damage (2 normal + 1 boosted for charging + 1 additional for Weapon Master + 1 additional for his feat).
"Living"
This is a word that most people often don't need help finding, but is important nonetheless. There are a lot of spells and effects that only affect living models. That means that constructs (Wolds, Warjacks, Immortals, etc.) or undead models won't be affected. Being non-living is a huge advantage due to the wide range of abilities that only affect living models. Make sure that awesome spell (or feat!) can affect the models you want it to before deciding on a plan of action.
"directly hit"
This will only be relevant with spells/attacks that have an AOE, but some effects will only trigger on a direct hit (Quake, Hex Blast) where a scattered blast would not. Other times, all that needs to happen is for a model to be 'hit' and that means that everyone in the AOE will receive the effect (like Continuous: Fire).
"friendly Faction" vs. "friendly"
Before taking that awesome Mercenary or Minion model with your awesome warcaster/warlock, make sure that your abilities will be able to affect them. Some factions, like Trollbloods, have a lot of spells and abilities that only affect their faction models, meaning you'll get less utility out of any Mercenaries or Minions. Some models, however, will count as Faction models under the right conditions, so pay attention to them! In particular, look for "X Ally" where they will be a faction model for X faction.
"Battlegroup"
This word is more important when you consider taking 'jack marshals, the Journeyman Warcaster, or lesser warlocks. Some spells will only affect members of your own battlegroup, so if there's a 'jack marshal with their own warjack, they're out of luck. Similarly, you might be able to upkeep spells (Absylonia, Magnus) on, use animi from (Doomshaper), or heal (Dr. Arkadius) models only in your battlegroup. Sometimes you can cast spells/animi on models which aren't a part of your battlegroup (Forced Evolution on Brine) for some advantage. Read carefully to consider all of your options!
"warjack/warbeast" vs. "warrior"
Some spells an animi will only affect warjack or warbeast models (Forced Evolution) while others will only affect warrior models (Storm Rager). Make sure you read carefully to see if the spell/animus can be cast on a variety of targets. Similarly, some spells will only deal damage to only warjacks/warbeasts (Spiny Growth, Sunhammer, pNemo's feat) while others will only affect warrior models (Iron Flesh).
"special attacks" vs. "special actions"
A special attack is a (* Attack) option and these can be performed if a model charges. This is the case with a lot of the "combo" attacks. Special actions, however, are listed as a (* Action) and cannot be performed after a charge move. This is the case with spell-casting infantry (like Battle Mages) or even the Menoth Castigator spewing flames. Some abilities and spells will prevent models from performing special attacks (Old Witch's feat) where others also prevent special actions (Zerkova's feat). Remember that power attacks are also special attacks!
"within" vs. "completely within"
As a Circle player, I see my opponents making this mistake all of the time. When a rule says "completely within" it means that each part of a models base must be completely within the distance specified. When the wording just says "within", any part of the model's base must be within the distance. Here's a practical example:
- Models move completely within their SPD value when making an advance.
- A warbeast must be within your control area in order to be forced.