Dictionary:

freakish

  (frē'kĭsh)

1. Markedly unusual or abnormal; strange: freakish weather; a freakish combination of styles.
2. Relating to or being a freak: a freakish extra toe.
3. Capricious or whimsical.

adjective

1. Deviating from the customary: bizarre, cranky, curious, eccentric, erratic, idiosyncratic, odd, outlandish, peculiar, quaint, queer, quirky, singular, strange, unnatural, unusual, weird. Slang kooky, screwball. British Slang rum, rummy². See usual/unusual.
2. Resembling a freak: freaky, grotesque, monstrous. See usual/unusual.
3. Following no predictable pattern: capricious, changeable, erratic, fantastic, fantastical, fickle, inconsistent, inconstant, mercurial, temperamental, ticklish, uncertain, unpredictable, unstable, unsteady, variable, volatile, whimsical. See change/persist, continue/stop/pause.

Definition: abnormal, unusual
Antonyms: common, general, natural, normal, ordinary, standard, usual

The adjective has 3 meanings:

Meaning #1: changeable
  Synonym: capricious

Meaning #2: characteristic of a freak

Meaning #3: conspicuously or grossly unconventional or unusual
  Synonyms: bizarre, eccentric, freaky, flaky, outlandish, outre