I have a UK C visit visa (multiple entry, valid for 6 months) that was issued in June 2017 for tourism. I made one visit, in June 2017, as a tourist. I need to make another visit in October 2017, but this time for an 8-day business trip (meetings and training at company's UK office). Can I use the visa? It is valid until December 2017?
There are some details about exactly what business activities are permitted by the visa at the link below. If you make sure that your planned activities are covered then it appears to me that you would be using the visa correctly. https://www.gov.uk/guidance/immigration-rules/immigration-rules-appendix-v-visitor-rules (What you wrote about your trip is not detailed enough to comment on whether it is within the rules)
You might not get caught. Or you might get caught, in which case your are in trouble right now, and for the future. It's not something I would risk. Since you met all the requirements to get a visitor visa, you should also be able to meet the requirements for a business visa without problems.