Almost always seen inside the four-character idiom 桀骜不驯 ('proud and untamable'), describing a strong-willed person who refuses to submit. Standalone use is rare and literary.
Top 敖 gives the sound (áo to ào, just a tone shift) and a faint flavor of 'roaming free,' fitting an untamed horse. Same phonetic appears in 傲 arrogant and 熬 to simmer.
