1Tough, formidable, hard to deal with — describing an opponent or problem that is strong and not easily overcome. This is the common reading of 手強い (てごわい); the same kanji is also read てづよい, with a different nuance.
決勝の相手はかなり手強いから、油断は禁物だ。
Our opponent in the final is quite formidable, so we can't afford to let our guard down.
この試験の応用問題は手強くて、時間内に解き終わらなかった。
The applied questions on this exam were tough, and I couldn't finish them in time.
交渉相手が思ったより手強く、話がなかなか前に進まない。
The other side in the negotiation was tougher than expected, so the talks made little headway.
あのチームは若手が多いが、守備が堅くて手強い。
That team is full of young players, but their defense is solid and they're formidable.