The word 'navvy' originated from the term 'inland navigator', used to describe those who built canals in Britain in the late eighteenth century. Later the word was used to describe the thousands of people who worked at building the railway lines, who were often Irish immigrants escaping poverty.
Navvies building the railways did labour-intensive work that required much physical strength. Today, the word is commonly used in Britain to describe those who do any kind of manual labour in the construction industry.