Something freaky is so weird that it's almost scary. If you have a freaky dream, you might wake with a frightened gasp.
Very strange looking animals are freaky, and creepy stories told at night around a campfire are best when they're a little freaky. An uncanny coincidence is freaky, and so are many Halloween costumes. The adjective is an informal way to say "bizarre" or "peculiar." It comes from freak, but the ultimate origin is unknown — although freak originally meant "a very sudden turn of mind."