What term is used to describe someone who is warlike in manner?

The term that accurately describes someone who is warlike in manner is "bellicose." This word derives from the Latin "bellicosus," which means "warlike" or "combative." It characterizes a person or attitude that is inclined to start conflicts or engage in aggressive behavior, highlighting a tendency toward hostility or militarism.

In contrast, the other options have different meanings: "animus" refers to a disposition or attitude, often with a sense of hostility but not specifically warlike; "ascetic" describes a lifestyle characterized by self-discipline and abstention from indulgence, often for religious or spiritual reasons; and "artless" means lacking art or knowledge, often in the context of simplicity or innocence. Each of these terms applies to different contexts and does not convey the specific notion of being warlike as "bellicose" does.