SAN FRANCISCO — U.S. District Judge Haywood Gilliam Jr. let lawyers for both Pinterest Inc. and Pintrips Inc. argue largely uninterrupted Monday morning as a bench trial got underway in the trademark spat between the social-media site and the Internet travel startup.

Pinterest, the nation’s third most popular online social-media site behind Facebook and Twitter, sued Pintrips in 2013 claiming the startup could have chosen any name, but intentionally selected one that is deceptively close to Pinterest’s. Pintrips, which has developed a tool to let users track airfares across multiple websites, has filed a counterclaim asking that Pinterest’s federally registered trademarks be canceled as generic.

Pinterest’s lawyer, Diane Doolittle of Quinn Emanuel Urquhart & Sullivan, said Monday morning the site’s 80 million users make it “one of the Bay Area’s great success stories.” Doolittle said Pinterest is “fanciful name” and the company pioneered the use of the word “pin” in relation to visually bookmarking digital content.

Doolittle pointed out that Pintrips was incorporated under a different name, Flightrax. By the time the name Pintrips was adopted in April 2012, Pinterest had 17 million active monthly users. “The folks at Pintrips knew well that their name was confusing,” Doolittle said. Pinterest is not seeking damages, but is asking for an injunction barring Pintrips from using its current name. “It is not an undue burden to ask Pintrips to rebrand,” Doolittle said.

Doolittle, who entered her first appearance as lead counsel for Pinterest in the case just last week, asked the judge and the court reporter to bear with her as she shifted back and forth between saying the two names, which sound quite similar when pronounced quickly in the manner she employed during her opening remarks. “It’s been a busy couple of days with a little less sleep than normal,” Doolittle said. The company’s prior lawyers at Harvey Siskind remain on the case, but had no speaking role during opening arguments.

Pintrips’s lawyer, Edward Colbert of Kenyon & Kenyon was much more deliberate in his pronunciation of Pinterest. (Think: Pin-TUR-est.) Colbert argued that people have used the terms “pin” and “pinning” in regards to digital information since the dawn of the Internet and before. He argued that the term has been used much like “trash,” “mail” and “folder” have been digitally, “as metaphors corresponding to their physical counterparts.”

“No company can monopolize those words for their common, ordinary uses,” Colbert said. Pintrips’ interface is very simple, Colbert said, and just posts compared flight times and prices and does “not post pictures of puppies or even pretty beaches.”

At one point, with Colbert edging into an argument about whether Pinterest is due a heightened level of trademark protection as a famous mark such as Kodak, Gilliam cut Colbert short.

“We don’t need a preclosing argument,” Gilliam said.

The bench trial is scheduled to continue through this week.

Contact the reporter at rtodd@alm.com.