Longman Dictionary of Contemporary English - improvement

~ n 1 an act of improving or a state of being improved + in  (There's certainly been an improvement in the children's behaviour.)  (We need to carry out some improvements to the computer system.) show an improvement  (This month's trading figures show some improvement. | room for improvement (=the possibility of improving even more))  (Your English is much better but there's still room for improvement.) 2 a change or addition that improves something  (Power steering is just one of the improvements to be found in the new 160cc model.) 3 be an improvement on to be better than something similar that existed before  (The new electronic controls are a big improvement on the old system.)