Is the development of decreasing sensitivity to a drug because of continued use; whereas is the development of decreasing sensitivity to a drug because of the use of another drug.

 The correct answer is :  Tolerance  ;  cross-tolerance

Explanation:  Tolerance occurs when a person is given a medication continuously and sensitivity to that substance decreases in the individual, that is, his body becomes accustomed to that medication. Cross tolerance occurs when a medicine produces tolerance not only to that medicine but also to another medicine similar to that which produces the same effect or that has the same functions.