strong; resolute; firm; strict
「手強い」 has another reading with different meanings.
difficult; tough; formidable; redoubtable; stubborn
彼女の意志は手強かった。
Her resolve was firm.
手強くて簡単には折れない人だ。
She's strong-willed and doesn't give in easily.
手強い信念を持つ人は尊敬に値する。
People with strong convictions deserve respect.