Cuil (/ˈkuːl/ KOOL) was a search engine that organized web pages by content and displayed relatively long entries along with thumbnail pictures for many results.

[6] The Irish ancestry of Anna Patterson's husband Tom Costello sparked the name Cuil, which the company states is taken from a series of Celtic folklore stories involving a character, Fionn mac Cumhaill, they erroneously refer to as Finn MacCuil.

Foras na Gaeilge, the official governing body of the Irish language, did not support the assertion that cuil means "knowledge".

[9] "I am unaware myself of the meaning 'knowledge' being with the word 'cuil' in Irish", Stiofán Ó Deoráin, an official on Foras na Gaeilge's terminology committee, said.

Dinneen only lists two nouns and one adjective with the spelling cuil: "f., a fly, a horse-fly...", "f., a venomous aspect; great eagerness..." and "gs.

[13] About one month after launch, Cuil's product VP and search technologist, Louis Monier, quit the company citing disagreements with the CEO, Tom Costello.

[21] Cuil worked on an automated encyclopedia called Cpedia, built by algorithmically summarizing and clustering ideas on the web[22] to create encyclopedia-like reports.

"[28][29] Cuil's VP of communications Vince Sollitto said the search engine was experiencing heavy first-day overloads and they were "busy putting out fires."

[33] Many website owners reported that the Twiceler crawler repeatedly hit their site with randomly generated URLs in an attempt to find pages inaccessible by links.