Facetious: treating issues with deliberately inappropriate humor; flippant. Plato.
Facile: (esp. of a theory or an argument) appearing neat and comprehensive only by ignoring the true complexities of the issue; superficial. (of a person) having a superficial or simplistic knowledge or approach.

Fastidious: very attentive to and concerned about accuracy and detail.

Fatuous: silly and pointless.

Festoon: adorn a place with chains, garlands, or other decorations.
Fiat: a formal authorization or proposition; a decree. An arbitrary order.
Filament: a slender threadlike object or fiber. Esp. one found in animal or plant structures.
Filch: pilfer or steal (something esp. of small value) in a casual way. (Proust. visits and excursions are so much time filched from the sea air.)
Fixity: the state of being unchanging or permanent. (Proust)
Florid: 1. Having a red or flushed complexion. 2. Elaborately or excessively intricate or complicated; (of language) using unusual words or complicated and rhetorical constructions.
Forgo: omit or decline to take (something pleasant or valuable); go without. Refrain from.
Fundamental: forming a necessary base or core; of central importance. Affecting or relating to the essential nature of something or the crucial point about an issue. So basic as to be hard to alter, resolve, or overcome.
Futile: incapable of producing any useful results; pointless.