Fess/fes/ Definition 1 of 2Pro Tip 1/3Colloquial Usage Use 'fess' in casual conversation, not formal writing or speeches. I need to fess to eating your leftovers. Pro Tip 2/3Expression of Guilt 'Fess' often shows someone is feeling guilty or ashamed about something. She fessed up to lying about her whereabouts. Pro Tip 3/3Confession Implication When you 'fess', you usually disclose something others are unaware of. He couldn't fess that he had lost the money.