The term 'second thought' can be defined as a DOUBT, QUALM, doubletake, RESERVATION, AFTERTHOUGHT, or delayed reaction. DOUBT is a feeling of uncertainty or lack of conviction about something, while QUALM is an uneasy feeling of DOUBT, worry, or fear. Doubletake is an act of looking twice at something, and RESERVATION is a feeling of DOUBT or hesitation about doing something. AFTERTHOUGHT is a thought that comes after an event has already happened, and delayed reaction is a reaction that occurs after a period of time has passed. All of these terms can be used to describe the concept of second thought.