The article identifies those groups of Estonian words whose etymology is essentially based on their areal distribution. Areal data are usually consulted to find out the chronological layer that the word belongs to. The areal criterion has a supportive, or even decisive function if certain loanwords are genetically too close to enable their differentiation according to the donor language of the stem (e.g. Germanic or Baltic, in the Estonian case). In Estonian etymological studies the areal criterion has been especially popular in differentiating between various Swedish loanwords. Due to the linguistic closeness of Finnic languages and a large number of shared vocabulary application of the areal criterion is often the only way to identify the possible substrate, superstrate and adstrate of closely related languages.