A shrinking violet
Definition 1 of 1
Pro Tip 1/3Emotional Connotation
Implies vulnerability or a lack of confidence, sometimes used compassionately. 
Even amidst boisterous debates, he remained a shrinking violet.
Pro Tip 2/3Informal Context
Used in casual conversation, less appropriate in formal writing or speeches. 
At parties, he's a bit of a shrinking violet.
Pro Tip 3/3Not Negative
Being a shrinking violet isn't always bad; it can mean being thoughtful and reserved. 
He's considered the office shrinking violet, calmly observing before he acts.