HITCH, SAY is a term used to describe the act of asking someone to marry you. It is derived from the phrase 'hitch your wagon to a star, ' which was popularized by Ralph Waldo Emerson in his essay 'Circles' and is often used as a metaphor for marriage. KNOT is the four letter solution to this crossword clue, and it is an appropriate answer because a KNOT is often used to symbolize the binding of two people in marriage.