Bellicose comes from the Latin adjectiv4 bellicosus ("of war", "warlike", or "fond of war"), and was derived from bellum ("war") and the suffix -osus ("full of" or "abounding in"), meaning "full of war" or "abounding in war" (eager to fight).  It entered English in the 15th century, describing someone aggressive, inclined to fight, or hostile, and shares roots with words like "belligerent" (an aggressive nation or person engaged in war or conflict) and "antebellum" (before the war). 

According to the Oxford English Dictionary (OED), the adjective bellicose first appeared in English during the Middle English period (1150-1500), with the earliest recorded use around 1432–50 in Higden's "Polychronicon".  

Examples of "bellicose" used in a sentence: 
"I've known many fighters, and most of them tend to be rather bellicose." 
"And people in charge of both governments have become more bellicose by the day." 
"Kholodov is a bear of a man, both friendly and bellicose, so their actions toward him have been comparatively cautious."  
"Never in peacetime, perhaps, have the statements of our government officials been more relentlessly bellicose."  
"In public he wasn't boisterous or bellicose – who did he need to impress with hard-guy posturing?" 
"These fervent and brutal but impractical dreamers were followed by hard-headed but less bellicose traders."