'Cinch' the deal or 'clinch' the deal?

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I thought this was going to be easy - a quick google and the answer would be obvious...but no...
So, which is it?
Need to know now as I have to email a writer and don't want to look thick!

clinch the deal

I don't know why, though! But 'cinch' means 'belt', and 'clinch' may be a variant of 'clench', as in handshake.

the scissor sisters would appear to think it is "cinch"...

maybe tis an american v english thing?

You clinch a deal.

Then on some American programmes you often here them talking about something being a "cinch," ie easy. Or have I made that up?

what puppymonkey said.

the return to oz song. on the first album...

"the patchwork girl has come to cinch the deal"

eether/eyther methinks

Another vote for clinch.

ok, will go with clinch!

I would have though "clinch"

Clinch the deal, cinch in your waist.