F

I am the abbreviation for Fahrenheit

I am the first letter in some words like foresight

Fantasy

Faculty

Fallacy

Failingly

Fatherly, and you will see me

Faithfully in words like fancy

Falsity

Fatally

Feelingly

Feudally

Foolishly

Forlornly

Formerly

Forwardly

Fussily

Me you see