Ask.com bought several reference sites including  Dictionary.com, Thesaurus.com and Reference.com in its acquisition of Lexico Publishing Group LLC.

Terms of the deal, set to be announced Thursday, aren’t being disclosed.

Dictionary.com is the most popular of the newly acquired reference sites, drawing 22.1 million visitors worldwide in March, according to comScore Inc. That represented a 20 percent increase from the same time last year.