The phrase "a fierce adversary" is correct and usable in written English.
You can use it to describe someone who is a strong opponent or competitor in a particular context, such as sports, debates, or conflicts.
Example: "In the championship match, she faced a fierce adversary who had trained rigorously for the competition."
Alternatives: "a formidable opponent" or "a tough rival."
Mr. Ellison, known as a fierce adversary, has used the case to attack Léo Apotheker, SAP's former chief executive and now chief executive of Hewlett-Packard.
That erotic attraction can be a fierce adversary is illustrated with electrifying aplomb by these two remarkable dancers in a breathtaking duet that begins at high intensity and builds from there.
Wenger, a fierce adversary for Ferguson during his early days at Highbury, joked he was "fearing the worst" before the release of the book, which the Arsenal manager maintains he still has not had time to read.
Pakistan's Supreme Court is causing further trouble for the prime minister, threatening to remove him from office for failing to comply with court orders to reopen long-ago corruption cases against President Asif Ali Zardari, himself a fierce adversary of the military.
The marches underscored the likelihood that California will be a fierce adversary if Trump follows through on his campaign promises to deport thousands of immigrants and build a massive wall along the U.S.-Mexico border. .
The sectarian rift has bedeviled Iraq since the 2003 U.S.-led invasion ousted ex-strongman Saddam Hussein, a Sunni who repressed Shiite and other opposition political movements and was a fierce adversary of Shiite Iran, Iraq's neighbor.
Lidington is hugely experienced, popular with his fellow MPs, and is a much more fierce adversary at the dispatch box than his twinkly persona might indicate.
Scott Walker, the governor of Wisconsin and a presumptive Republican Presidential candidate, is a fierce ideological adversary.
Now Dwayne Bravo, another key figure in West Indies T20 success but the board's longest and most fierce adversary, has added fuel to the flames with his own scathing attack on Cameron during an interview with CNC3, a Trinidad and Tobago television network.
Yet for a pair of companies that are such fierce adversaries, Microsoft and AOL actually compete very little -- at least today.
In its ongoing quest for a balanced budget, Quebec's government has taken on some pretty fierce adversaries.
