Long duration is a term used to describe something that lasts for a considerable period of time. However, there are several synonyms that can be used to express similar concepts. For instance, the expression 'prolonged period' could be used to indicate a time span that is extended. The term 'lengthy term' could also be used to describe a situation that endures over a long period of time. Similarly, 'extended lifespan' and 'long-lasting' are other synonyms that can be used for long duration. Moreover, expressions like 'extended timeline,' 'extended period,' 'extended interval,' and 'extended time' could also be used to describe something that takes a prolonged amount of time.