noun which may take the genitive case particle 'no'
on the gentle side; somewhat meek; rather quiet
Describes a person or demeanor that is somewhat gentle, meek, or quiet compared to others; often used when making a relative comparison.
See also: おとなしい
彼はクラスの中ではおとなし目な方だ。
He is on the quiet side in his class.
今日はおとなし目の服を選んだ。
I chose rather subdued clothes today.
おとなしい means 'gentle, quiet, obedient' as a standalone adjective. おとなし目 adds the nuance of 'on the ... side' or 'somewhat', making it a comparative expression.
Derived from the adjective おとなしい (gentle, quiet) by adding the suffix 目 (め), which indicates a tendency or degree ('on the ... side').