Using a spell isn't defined anywhere in the rules. Given the natural language style of 5e it could just as easily be a reference to casting a spell as using a spell in some non-casted manner.
The verbiage used for "When you cast a spell of X, then Y happens" is fairly uniform.Can anyone point to examples where a change of verbiage for these types of abilities is Just Natural Language?
The Storm Sorcerer has an ability that triggers when they start casting a spell.
The intent, even when conveyed through natural language, is clear.
Disciple of Life states this:
Also starting at 1st level, your healing spells are more effective. Whenever you use a spell of 1st level or higher to restore hit points to a creature, the creature regains additional hit points equal to 2 + the spell's level.
Aura of Vitality states this:
You can use a bonus action to cause one creature in the aura (including you) to regain 2d6 hit points.
By any, reasonable, Natural Language standard, Aura of Vitality, is being used when initially cast, and later when the player uses Aura of Vitality and their character's Bonus Action to heal hit points.
Aura of Life...is Concentrating on a spell using it? No.
Yet, when Aura of Life does heal someone, by Natural Language, you have just used the spell.
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