Noun

1. A sudden causeless change or turn of the mind; a whim of fancy; a capricious prank; a vagary or caprice.
2. An oddball, especially in physiology; unique in a displeasing way.
3. A person whose physique has grown far beyond the normal limits of muscular development; often a bodybuilder weighing more than 120 kilos (260 pounds).
4. A person who has an obsession or extreme knowledge of a something.
5. A very sexually perverse individual, usually used affectionately or in another good willed context.

Verb

1. To make greatly distressed and/or a discomposed appearance
   • 1994, James Earl Hardy, B-Boy Blues: A Seriously Sexy, Fiercely Funny, Black-On-Black Love Story, (Alyson Publishing), page 107

     But after one night turned into five days, I was freaking out. I missed him.

2. To be placed or place someone under the influence of a psychedelic drug
   • 1992, Peter G. Stafford, Psychedelics Encyclopedia, (Ronin Publishing), page 56

     "[...] Harvard have compiled a list of LSD's contributions—largely missing before then—to our popular language: turned on, straight, freak, freaked out, stoned, [...]"

3. To streak
   • 1930, Robert Seymour Bridges, The Testament of Beauty: A Poem in Four Books, (Literary Criticism), page 20

     "[...] in fine diaper of silver and mother-of-pearl freaking the intense azure; Now scurrying close overhead, wild ink-hued random racers that fling sheeted [...]"

4. To experience reality withdrawal, or hallucinations (nightmarish), to behave irrational or unconventional due to drug use.
5. To react extremely or irrationally, usually under distress or discomposure