It is true that people smoke to consume nicotine. Many people report that nicotine brings them benefits. It can offer relief from stress or help focus attention. This can make it difficult for people to stop smoking. So, in this sense, nicotine is ‘addictive’. 

However, the word ‘addiction’ is often associated with chronic use of drugs like heroin or crack. It is ridiculous to think about nicotine in those terms. Addiction can be defined as dependent use plus harm. As there is very little if any harm associated even with long term use of nicotine, it would be more realistic to think about the nicotine ‘habit’ or ‘dependence’ rather than ‘addiction’.