Search firm Ask.com is to acquire Lexico Publishing Group which owns Dictionary.com, Thesaurus.com and Reference.com.

Figures from traffic monitor comScore suggest that more than 500 million monthly worldwide searches consist of dictionary, thesaurus and encyclopaedia queries.

Ask.com claims that Lexico's demographics are nearly identical to its own, and that this is a good opportunity to push traffic between both user bases.

The search company reckons that the acquisition will grow its user base by around 11 per cent to more than 145 million monthly unique users.

This would rank Ask Network as the ninth largest web property in the world, ahead of Apple and Facebook.

"More than 30 per cent of all searches conducted on Ask.com are in the reference category. 'Dictionary' was the second-most searched term on Ask.com in 2007," said Jim Safka, chief executive of Ask.com.

"At the same time, Lexico's consumers frequently seek out a search engine immediately before and after using one of Lexico's sites. This acquisition expands Ask.com's reach and aligns perfectly with our customers' needs."

Exact terms of the all-cash transaction were not disclosed.