• the brush of,
• the bruch off,
• the bruch-of,
• teh brush-off,
• the brushoff,
• the rush-off,
• the brush-ofd

The adjective form of "the brush-off" is "brushed-off".

The plural form of "the brush-off" would be "the brush-offs".

The singular form of the word "the brush-off" is "the brush-off". The word does not change when going from plural to singular.