Multiple realities
(covers information from several alternate timelines)
A decade was a time period of ten years.
According to Sub-commander T'Pol, the soil and foliage of Terra Nova would be irradiated for at least another decade as of 2151. (ENT: "Terra Nova")
Travis Mayweather told T'Pol at dinner in the captain's mess that Earth spent years and decades to solve the mysteries of Amelia Earhart and Judge Crater. (ENT: "Terra Nova")
According to Trip Tucker in the mirror universe, a Human lost a decade off their life expectancy for every year spent working near a warp core. (ENT: "In a Mirror, Darkly")