Etymology can be a useful tool in literary analysis; however, it needs to be used with a sense of how words and their meanings evolve. More often than not, if one merely scours an etymological dictionary for an "original" meaning, the results are neutral, if not indeed counter-productive.
An example is Homeric achreion. Used only twice in Homer, at Iliad 2.269 and Odyssey 18.163, this word looks like a negative compound of a "un-" + chreos "use". The resulting meaning "useless", though, does not work very well in Homer. In particular, such an interpretation at Odyssey 18.163 gives us a relatively weak Penelope, who can only react helplessly to the Suitors' importunings. The rest of the scene, though, shows her deftly manipulating them.
Currently, the most widely accepted view of the phrase achreion egelassen "she laughed in an achreion fashion" at Odyssey 18.163 is that achreion here means something like "inappropriately" or "uncharacteristically" (so Clay, American Journal of Philology 105 [1984] 73-76). Such a development from "uselessly" seems difficult, but it is, faute de mieux, accepted by Russo in Heubeck, A Commentary on Homer's Odyssey (Oxford, 1992), 3.59.
In place of a derivation from a + chreos, I propose a derivation of achreion from achri "until". A resulting nuance, then, would be something like "wait and see". At Odyssey 18.163, for example, Penelope's laugh is a signal that her attendants should simply wait until they see how things turn out: she is going to trick the Suitors into bringing her costly gifts, even as she has no intention of marrying any of them.
In post-Homeric Greek, on the other hand, most uses of achreion reflect an analysis in terms of a + chreos. The reason may be that, although the form achri is frequent in Homer, it is later more familiar as mechri, with, apparently, full-grade me- instead of a- from a zero-grade vocalic nasal *m-. Even so, at least one later use of achrei- shows the Homeric analysis. At Cratinus, fr. 323, the judgment of "tomorrow's critics" is described with the adverb achreiogelos "laughing in an achreion fashion". Presumably, "tomorrow's critics" will judge more accurately than those who come to a quick and superficial judgment; correspondingly, they are better described as waiting until they have the last laugh than as acting "helplessly" or "inappropriately".