大放厥词 is a four-character idiom (chengyu) that literally means 'to greatly let loose one's words.' It is used to describe someone who makes wild, boastful, or absurd statements — often with a critical tone. The word '厥' is an archaic possessive ('his/her/its'), but you don't need to analyze it; just remember the phrase as a fixed expression for 'talking nonsense' or 'bragging excessively.' It is typically used in formal or written contexts to criticize someone's speech.