难以

The problem became more difficult to solve.

Her life is still in doubt.

The match holds fond memories for me.

Words fail to express the depth of anger. / Anger is beyond words.

elusive; impalpable

beyond belief; unbelievable; incredible; difficult/hard to believe

unable to feed one's family

beyond imagination/hard to imagine

hard to get along with

hard to bear/stand

beyond/past comprehension

hard to accept

unable to feed oneself

difficult to appraise/measure/evaluate/assess; inestimable