I use a lot of software, some of which costs a lot of money, yet doesn't work they way I wish. (Yes, I'm dissing you, Microsoft). I'm delighted when I find a program that does just what I need, and for free. One that I use constantly is the excellent WordWeb.
Wordweb is a dictionary/thesaurus that you can download to your PC so that, even when offline, you can pull up definitions and synonyms with a single ctl-right-click. I've found Wordweb's lexicon broader and better defined than what is included with Microsoft Word, and quicker to access.
Best of all, Wordweb is a free download for most of us, thanks to the largess of its designer, Antony Lewis. An expanded version, Wordweb Pro, for $29 offers more words, pronunciations, and a more polished wild-card utilizing search function. Both versions are free of spyware and other annoying crap.
A caveat- One unusual feature of Wordweb is that Lewis requires anyone that takes more than two commercial air flights per year to upgrade to Wordweb Pro. This is his way of raising awareness of the environmental costs of such travel, and asking for money from those who can presumably afford it ,while keeping it free for those who can't.