If something that someone does costs them dear, they suffer a lot as a result of it. Such complacency is costing the company dear. Severe; grievous; sore: our dearest need
feelings You can use dear in expressions such as `oh dear', `dear me', and `dear, dear' when you are sad, disappointed, or surprised about something. `Oh dear, oh dear.' McKinnon sighed. `You, too.'
earnest; "one's dearest wish"; "devout wishes for their success"; "heartfelt condolences"
Dear is written at the beginning of a letter, followed by the name or title of the person you are writing to. Dear Peter, I have been thinking about you so much during the past few days