“ADDITIVITY” is a valid word.

dittya short simple song (or the words of a poem intended to be sung)
davita crane-like device (usually one of a pair) for suspending or lowering equipment (as a lifeboat)
vitta

tidyreceptacle that holds odds and ends (as sewing materials)
davyEnglish chemist who was a pioneer in electrochemistry and who used it to isolate elements sodium and potassium and barium and boron and calcium and magnesium and chlorine (1778-1829)
divaa distinguished female operatic singer; a female operatic star
vita
avid(often followed by `for') ardently or excessively desirous
tititree of low-lying coastal areas of southeastern United States having glossy leaves and racemes of fragrant white flowers
dyadtwo items of the same kind
ditaevergreen tree of eastern Asia and Philippines having large leathery leaves and small green-white flowers in compact cymes; bark formerly used medicinally
adita nearly horizontal passage from the surface into a mine
didy
tivy

didengage in
daytime for Earth to make a complete rotation on its axis
dadan informal term for a father; probably derived from baby talk
adda condition (mostly in boys) characterized by behavioral and learning disorders
aida resource
via
ivyOld World vine with lobed evergreen leaves and black berrylike fruits
tada slight amount or degree of difference
titeither of two soft fleshy milk-secreting glandular organs on the chest of a woman
tattastelessness by virtue of being cheap and vulgar
vata tax levied on the difference between a commodity's price before taxes and its cost of production
att
ditthe shorter of the two telegraphic signals used in Morse code
yid(ethnic slur) offensive term for a Jew
ait
tav

itthe branch of engineering that deals with the use of computers and telecommunications to retrieve and store and transmit information
ata highly unstable radioactive element (the heaviest of the halogen series); a decay product of uranium and thorium
ya
ida state in the Rocky Mountains
ada public promotion of some product or service
ay
taa hard grey lustrous metallic element that is highly resistant to corrosion; occurs in niobite and fergusonite and tantalite
aian agency of the United States Army responsible for providing timely and relevant and accurate and synchronized intelligence to tactical and operational and strategic level commanders
tia light strong grey lustrous corrosion-resistant metallic element used in strong lightweight alloys (as for airplane parts); the main sources are rutile and ilmenite

ADDITIVITY