NEW YORK (Reuters) - Retailers who saw strong online sales at the start of the holiday shopping season this weekend aim to cash in further on that momentum with Cyber Monday, one of the biggest days for Web commerce.

The term Cyber Monday was coined five years ago for the day many people return to work after U.S. Thanksgiving Day and make online gift purchases on their computers.

More recently, retailers have been increasingly offering online deals on Thanksgiving itself and through the holiday weekend, as consumers regularly shop on the Internet.

Online spending on last Thursday's Thanksgiving Day rose 28 percent from a year ago to $407 million, according to analytics company comScore. ComScore has forecast overall online sales for the holiday season, when most shopping is done between Thanksgiving and Christmas on December 25, to rise 11 percent to $32.4 billion.

"The trends today should follow what happened over the weekend," said Maggie Taylor, a senior credit officer with Moody's. "I would expect Cyber Monday to be as strong as sales were this weekend." Those early returns helped boost shares of Web commerce companies, with industry leader Inc rising as much as 2.6 percent early on to an all-time high at $181.84, though the shares were up just 0.6 percent by midday. shares were up 2 percent while Blue Nile was up 5.6 percent compared with a decline of 1.1 percent in the Standard & Poor's 500 Index.

According to the National Retail Federation, about 33.6 percent of people who went shopping during the four-day holiday weekend bought goods online, up 15 percent from a year ago.

The amount they spent is up as well. The trade group estimates that out of the $365.34 spent by the average consumer this weekend, $121.67, or 33.3 percent, was spent online. That is up from 30.2 percent last year. At the same time, the early deals on offer could eventually chip away at "Cyber Monday" as an event on the calendar, some analysts said.

"At this point, Cyber Monday could be relegated to the scrap heap in terms of importance for retailers," said Wall Street Strategies analyst Brian Sozzi in a research note. In a survey conducted over the weekend by America's Research Group, a consumer research firm, only 18.1 percent of those polled said they would be buying online on Monday, compared with 25 percent a year earlier.

That could reflect the fact that many consumers already did their shopping over the weekend, said group president Britt Beemer.

Traditional retailers are also competing more fiercely for online sales, with Wal-Mart Stores Inc going head-to-head with Amazon on free shipping of merchandise during the holidays.