The term 'in single file' refers to a formation in which people or objects are arranged in a line, one behind the other. This formation is often used when marching or walking in a group. The crossword solutions for this term are 'TANDEM' (6 letters), 'onebyone' (8 letters), 'oneatatime' (10 letters), and 'oneafteranother' (15 letters). All of these solutions describe the same concept of arranging people or objects in a line, one behind the other.