“SIZIEST” is a valid word. — 16 points Scrabble

sizethe physical magnitude of something (how big it is)
sitethe piece of land on which something is located (or is to be located)
setsa group of things of the same kind that belong together and are so used
tiesneckwear consisting of a long narrow piece of material worn (mostly by men) under a collar and tied in knot at the front
sitsbe seated
zestvigorous and enthusiastic enjoyment
zitsa small inflamed elevation of the skin; a pustule or papule; common symptom in acne
zitimedium-sized tubular pasta in short pieces
seis

sitbe seated
its
seta group of things of the same kind that belong together and are so used
tieneckwear consisting of a long narrow piece of material worn (mostly by men) under a collar and tied in knot at the front
sisa female person who has the same parents as another person
tis
zita small inflamed elevation of the skin; a pustule or papule; common symptom in acne
sei
ess

itthe branch of engineering that deals with the use of computers and telecommunications to retrieve and store and transmit information
ishave the quality of being; (copula, used with an adjective or a predicate noun)
et
sia tetravalent nonmetallic element; next to oxygen it is the most abundant element in the earth's crust; occurs in clay and feldspar and granite and quartz and sand; used as a semiconductor in transistors
esa radioactive transuranic element produced by bombarding plutonium with neutrons
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

SIZIEST