straightener

What it means

1. A pair of metal tongs with heated ceramic plates used for straightening hair.
2. Anyone or anything which straightens.
3. slangA prearranged fight to settle a dispute.

In a sentence

'Injection or not, the bloody thing won't move an inch with juice and it ain't got any. Yeah and here comes the law.' Cool as a cucumber, Ernie said, 'Leave him to me. I'll give him a straightener.'

2001, William F. Gray, The Villain, page 65

Where it comes from

From straighten + -er.