* 'good, preferable'
* 'adjustment (by addition and subtraction)'
* literally 'make/leave it to the right/reasonable/acceptable/tolerable degree'
can also be used with a negative connotation with the meaning "sloppy" (almost opposite of the original meaning) as in the sentence given in yadokari's comment to this question. As for why, that may be a good independent question; there are some other words like that.