This word is acceptable for play in the US & UK dictionaries that are being used in the following games:

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ad. In a vain manner; to no avail.

ad. In a vain manner; in vain.

In a vain manner.

In an inflated or conceited manner; proudly; arrogantly: as, to strut about vainly.

Idly; foolishly; unreasonably; hence, erroneously; falsely.

ad. to no avail

"While the woman goggled at me, her brain vainly attempting to take precious processing cycles away from analyzing reality TV to comprehend what had just been said to her, I stepped around her, handed my jar of salsa to the cashier, and completed my purchase."

in vain   

humanely    mainly    plainly    ungainly