Fallacy of four terms (quaternio terminorum)

Biological Parallel

'All cats are felines. All felines are carnivores. Tigers are cats. Therefore, tigers are carnivores.' Seems valid—but 'cats' shifts meaning (domestic cats vs Felidae family). This equivocation creates four terms masquerading as three. In evolutionary biology: 'fitness' means reproductive success, but also immune function, survival, mating success—each subtly different. Arguments using 'fitness' in shifting senses commit the four-term fallacy. Definitional drift invalidates logical chains.