Is it permissible to listen to a woman's singing if the song is devoid of forbidden words and flirtation, and the woman's voice is not arousing to men?

It is not permissible for a man to listen to a woman's singing, even if her singing is free of forbidden speech and music. This is because her singing for men invariably involves softening and beautifying the voice, which falls under the category of "speaking in a submissive manner" (khudu' bil-qawl), which is prohibited.