Final answer:
The word 'innocuous' in the sentence means harmless or non-threatening.
Step-by-step explanation:
The word innocuous is used in the given sentence to describe a smile that is harmless, inoffensive, or non-threatening. It implies that women are expected to wear a smile that does not cause any trouble or discomfort to others.
In this context, an 'innocuous smile' refers to a smile that is seen as socially acceptable but may not represent the true emotions of the women.