Quatreme

Quatreme (q or qat), also known as fourth (f), is a equal to  of a, 0.2 s, or  of a tierce. Quatreme comes from the French word quatrième, meaning "fourth", because this unit is two steps in magnitude from second. I chose French as the origin of this word since it has 'treme' embedded in it that would seem to be a portmanteau of quarter and extreme as this is the smallest unit of the series of units in factors of 60 from other units that includes hours, minutes, seconds, tierces, and quatremes.

The Earth's day is lengthening by 6.5 quatremes per century.