Ask.com, the fourth-ranked search engine, has completed its acquisition of Lexico Publishing Group, which owns Dictionary.com, Thesaurus.com, and Reference.com.

Ask.com, a wholly owned subsidiary of InterActiveCorp, had announced the all-cash deal in mid-May. Financial terms of the deal, which closed Thursday, were not released. Lexico, a privately held company based in Long Beach, Calif., debuted in 1995 with Dictionary.com.

Altogether, Dictionary.com, Thesaurus.com, and Reference.com had more than 28 million unique visitors in March, according to Lexico.

In May, Ask.com said the acquisition would increase its unique monthly users by 11 percent to 145 million.

According to statistics-tracker Hitwise, Ask.com had 4.23 percent of the U.S. search market in May. Microsoft had 5.89 percent, Yahoo had 19.95 percent, and Google overwhelmed them all with 68.29 percent.