If something is freaky, it is strange or unusual in a way that gives you a small fright or an uneasy feeling — a freaky noise at night, a freaky coincidence, a freaky smile on an old doll. It is more spoken and casual than freakish; younger speakers use it a lot. It can be light (“that’s a bit freaky”) or genuinely creepy, depending on the voice. Though actually, in informal American English the same word is also used about sex — “getting freaky” — which has nothing to do with being frightened. Same spelling, different street meaning; the “strange / a bit frightening” sense is the one you want in careful writing. Tone: informal. You would probably not put it in a school essay unless you were quoting speech.