Fantastic-alness (n.)
definition: The quality of being fantastic.

Fantastic-alness is a 16 letter word that begins with a F and ends in an S

Feather-brained/ (a.)
definition: Giddy; frivolous; feather-headed.

Feather-brained/ is a 16 letter word that begins with a F and ends in a /

Flabbergastation (n.)
definition: The state of being flabbergasted.

Flabbergastation is a 16 letter word that begins with a F and ends in an N

Forisfamiliating (p.)
definition: of Forisfamiliate

Forisfamiliating is a 16 letter word that begins with a F and ends in a G

Forisfamiliation (n.)
definition: The act of forisfamiliating.

Forisfamiliation is a 16 letter word that begins with a F and ends in an N

Fraunhofer lines
definition: The lines of the spectrun; especially and properly
The dark lines of the solar spectrum so called because first accurately observed and interpreted by Fraunhofer a German physicist.
Fraunhofer lines is a 16 letter word that begins with a F and ends in an S

 1