The term 'up in arms' is used to describe a situation in which people are very ANGRY and HOSTILE. This can be seen in the crossword solutions, which include words such as 'INDIGNANT' (9 letters), 'IRATE' (5 letters), 'ANGRY' (5 letters), 'HOSTILE' (7 letters), 'MILITANT' (8 letters), 'LIVID' (5 letters), and 'FURIOUS' (7 letters). Additionally, the word 'enlisted' (8 letters) implies that people are actively taking part in a cause or movement, suggesting that they are willing to fight for what they believe in.