Adwords says one click, but analytics says 0 visitors?
There is a good and comprehensive explanation on that in the help center. Please read here;
Did you find any helpful responses or answers to your query? If yes, please mark it as the ‘Best Answer’
As the help documentation cited by Moshe, clicks in the adwords interface are not equal to visits in analytics, for multiple potential reasons. I do wonder, what kind of click was this? If for example, you have call extensions enabled, and this was a click to call click from a mobile device, that click would not register as a visit in analytics, because the click never resulted in a visit to the site. This may not be the reason at all, but is just another example of why these two numbers don't always match up 100%.
If you have auto tagging enabled for your analytics profile, you should be able to find adwords data as a seperate tab in the analytics interface. Take a look at the clicks tab, and see if you can find out why that click was not reported as an analytics visit. If s a user immediately leaves the site, before the site loads for example, that's still a click on the ad, but if the page load time is too slow, the user could bail before acttually getting to the site.