What's the difference between 秒钟 and 秒? Both of them seem to mean a second, according to both wiktionary and linedict.

https://en.wiktionary.org/wiki/秒钟#Chinese

https://en.wiktionary.org/wiki/秒

http://ce.linedict.com/dict.html#/cnen/entry/b90b963dcf6f45cead8a742525cd059f
If we're only talking about the English word second, then 秒钟 and 秒 don't really have any difference.

Perhaps you could think of 秒 as sec, as in give me sec or I'll be there in a sec &amp; 秒钟 as second.

If we check out MDBG's definition of 秒 we can see that it also includes other things beside a measurement for time, like:


  arc second (angular measurement unit)


and 


  (coll.) instantly 


Otherwise for general purposes: 秒钟 is just the lengthened form of 秒 &amp; 秒 is just the shortened form of 秒钟.