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difficult; tough; formidable; redoubtable; stubborn
今回の相手は手強かった。
This time's opponent was tough.
その問題は手強くて苦労した。
That problem was tough and gave me a hard time.
手強い相手ほど倒した時の喜びは大きい。
The tougher the opponent, the greater the joy of winning.