Insidious
Sneaky
Insolent
Arrogant
Integral
Essential
Intrinsic
Inherent
Irascible
Easily angered
Judicious
Exercising sound judgement
Lament
To mourn
Laud
To praise
Malignant
Causing harm
Mendacious
Lying
Mitigate
To moderate the effect of something
Mollify
To soften
Mundane
Ordinary
Myriad
A huge number
Nefarious
Evil
Notorious
Famous for something bad
Noxious
Harmful
Obdurate
Stubborn
Obscure
Unknown
Onerous
Oppressive