Wisp (noun)

1. A small bunch or bundle, especially of twigs or grass used as a torch.
2. A small, slender, or delicate person or thing.
3. A small, faint, or fleeting trace or hint of something.

Origin:

Middle english wisp, from old english wisp; akin to old high german wispf wisp.

Examples:

1. The wisp of smoke rose from the campfire.
2. She was a wisp of a girl, fragile and delicate.
3. He caught a wisp of a scent in the air.
4. The wisp of hair that fell across her forehead was the only sign of disarray.
5. The wisp of a cloud was all that remained of the storm.