@M.A.R. The Single Word Request tag indicates that a single word answer is applicable. Sometimes it's combined with
phrase-requests or similar if people don't care whether their answer is not really a single word, as with the word request tag on E.L.U., and many of the questions which lack that tag should probably have it, esp. based upon accepted answers. However, some questions
are legitimately
single word requests, which makes it a little difficult to ascertain a universal rule.