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

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v. Present participle of endeavour.

"I, who had ever been surrounded by amiable companions, continually engaged in endeavouring to bestow mutual pleasure, I was now alone."

endeavoured    endeavouring    endeavours   

strive   

Trevor    bever    clever    endeavor    ever   

endeavor    exertion    devotion    aspiration    labors