This word is acceptable for play in the UK dictionary that is being used in the following games:

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v. Simple past tense and past participle of concentre.

"Flat upon the ground, the small army concentred on the igloo, and behind, deliciously expectant, crouched many women and children, come out to witness the murder."

concentred    concentring   

align    adjust    line-up    aline   

refocus   

concentric