Bards of the College of Swords have a feature called Blade Flourish that lets them use their Bardic Inspiration to add a modifier to their Attack action (XGtE, p. 15):
Whenever you take the Attack action on your turn, your walking speed increases by 10 feet until the end of the turn, and if a weapon attack that you make as part of this action hits a creature, you can use one of the following Blade Flourish options of your choice.
The feature then goes on to read:
You can use only one Blade Flourish option per turn.
Does this last clause mean that you can only use the feature to affect one attack in that turn, or that you can only use one of the three options for any attack you wish to affect during that turn?
For example: Could I hit my first attack and choose to use Mobile Flourish, and then hit a second attack in the same turn and expend a second usage of Bardic Inspiration to use Mobile Flourish again?
Best Answer
Only one attack can be modified by a Blade Flourish
There is another Q/A regarding the sorcerer's Metamagic which states:
There is now a small semantic requirement/argument that "you can use only one metamagic option on a spell" and "you can use only one metamagic option per spell" are equivalent statements.
To me this is true and so the above sentences are equivalent. This sentence structure was ruled in the Sage Advice Compendium to mean that you cannot use the same metamagic option multiple times per casting:
The Bard's Blade Flourish feature has the same structure stating:
It should follow the precedent set forth by metamagics and the Sage Advice Compendium and so the Blade Flourish clause means that you cannot use the same Blade Flourish option multiple times per turn.
To spell this out more directly:
You can use a metamagic option once per spell casting, and you can't use the same one multiple times in a spell casting.
You can use a Blade Flourish option once per turn, and so you can't use the same one multiple times in a turn.
This is also supported by Jeremy Crawford (though now unofficial, and at best can only be considered rules as intended) here stating:
A small note on wording: Blade Flourish does not say that you can use it once per attack because then you could use different Flourishes with each attack.
Only one attack can be modified by one Blade Flourish option per turn.