Deleterious is an adjective used to describe something or someone as dangerous or causing injury, usually in an unobtrusive or surprising manner.
The adverb form is deleteriously, and the noun form is deleteriousness.
Detrimental is also an adjective used to describe something or someone as dangerous or causing injury, usually in an obvious or expected way.
The adverb form is detrimentally, and the noun form is still detrimental.
Examples
This suggests that work-study programs give students a small piece of responsibility for funding their college education, and thus incentive to study harder, while if parents assume all of the cost it can have a deleterious effect on academic motivation. [The Wall Street Journal]
Obama said that if the FCC reclassifies Internet service under Title II of the Telecommunications Act to treat it as a utility, the agency will be better positioned to protect equal access to information and to ensure huge Internet service providers don’t dominate the market deleteriously. [Slate Magazine]
Calderon-Garciduenas said that there was a 50-year window of opportunity between the time urban children experience the detrimental effects and when they will present with mild cognitive impairment and dementia, and hence urgent action should be taken focusing on APOE e4 and air pollution interactions impacting children’s brains, as their responses could provide new avenues toward the unprecedented opportunity for Alzheimer’s disease prevention. [Business Standard]
At the same time they have been carefully designed to avoid cost to the taxpayer and to avoid detrimentally affecting the provision of services to current members. [The Telegraph]