The word biosynthesises is playable in Words With Friends™, no blanks required. Because it is longer than 7 letters, you would have to play off an existing word or do it in several moves.
Words With Friends™ Letter Score: 22
Highest Scoring Words With Friends™ Play In The Letters
Seven Letter Word Alert: (31 words)
benthos, biotins, boneset, boniest, byssine, ebonies, ethynes, eyeshot, hessite, hissies, histone, honesty, hostess, hotness, inosite, insists, ionises, isohyet, niobite, nosiest, obesity, osseins, seitens, session, sestine, shyness, sissies, stenose, stonish, syenite, thiones