1 difficult

2 challenging

3 straitened circumstances

4 difficult situation

1 to test (machinery etc)

2 to test (students)

3 test

4 quiz

5 exam

6 beta (software)

1 difficult (to...)

2 problem

3 difficulty

4 difficult

5 not good

1 hard to (predict, imagine etc)

1 to feel unwell

2 to suffer pain

3 to be difficult to bear

1 lit. An interval of time is worth an ounce of gold, money cannot buy you time. (idiom)

2 fig. Time is precious and must be treasured.

1 lit. a single post cannot prop up a falling house (idiom)

2 fig. one is helpless alone

1 lit. once said, a team of horses cannot unsay it (idiom); a promise must be kept

1 hard to explain in a few words (idiom); complicated and not easy to express succinctly

1 there is nothing the determined person can't accomplish (idiom)

2 persistence will overcome