Survey respondents may misinterpret the questions they are asked, potentially undermining the accuracy of their answers. One way to reduce this risk is to make definitions of key question concepts available to the respondents. In the current study we compared two methods of making definitions available to web survey respondents – displaying the definition with the question text and displaying the definition when respondents roll the mouse over the relevant question terms. When definitions were always displayed they were consulted more than when they required a rollover request. The length of the definitions did not affect how frequently they were used under either method of display. Respondents who completed training items designed to encourage definition use actually requested definitions less often, suggesting that they may value minimal effort over improved understanding. We conclude that at least for small numbers of questions, providing definitions with the question is likely to be the more effective approach than rollovers or hyperlinks.