The phrase "in arms" can refer to a person who is bearing weapons or actively fighting in a physical war or conflict. Synonyms for this phrase include "armed," "battle-ready," "combatant," and "soldiering."
However, "in arms" can also refer to a person who is holding or embracing something or someone tightly. Synonyms for this usage include "embracing," "clutching," "hugging," and "clasping." Additionally, "in arms" can be used to describe a person who is actively supporting a cause or working diligently towards a goal. Synonyms for this usage include "committed," "invested," "devoted," and "enthusiastic."
In summary, the phrase "in arms" can have multiple meanings and connotations depending on context, and various synonyms can be used to convey these different meanings.