"Al tonu ish es achiv..." (25:14)
"V'lo tonu ish es amiso..." (25:17)
Chazal derive from the repitition of the issur ona'ah that there are two parts to the prohibition: (1) ona'as mamon, to overcharge on an item; (2) ona'as devarim, 'harmful words', for lack of a better way to translate. The Mishna (B.M.58) gives an example of the latter in a case where one reminds a ba'al tshuva or a ger of their past ways, causing them pain. The gemara also includes under this prohibition a case of shopping in a store with no intent to buy - the salesperson is misled to devote time and energy on the shopper, all for naught. I was wondering recently why this aspect of the issur is not included under the general framework of gneivas da'as - perhaps it is, but the gemara seems to spell it out only in the ona'ah context.
Just wanted to highlight what I think is the most practical aspect of this issur - the gemara itself delivers a special warning to be careful of ona'as devarim with respect to how one speaks to one's wife (and no, my wife did not force me to write that : )