'Overly' is an adverb that means 'excessive' or too much. Similar in meaning to 'excessively', 'unduly' or 'inordinately'. 

1. The child was overly possessive of her dog, and wouldn't let anyone else play with him.
2. After five years working there, the employee had become overly comfortable in her role and struggled for motivation. 

1. You should never be overly comfortable in your role, you should always strive to perform better and make improvements.
2. Some people make the mistake of being overly comfortable with clients and treat them as a friend.