(By thread count)
Febrile - used twice in the last year and several more prior.
Flotsam - came close, though 6 times.
Flocculent - used once. Ever. But 4 years ago.
Effervescent - used 4 times in the last year.
Effervesce - however, used twice in the last year, but only four times total.
Exfoliate - used 4 times in the last year.
Coagulate - used 3 times in the last year.
Spiracle - used only twice ever, neither in the last year.
Pith - used 3 times in the last year.
Surfactant - used 5 times in the last year.
Hydrophobic - used 5 times in the last year.