The term 'clammed up' is a phrase used to describe someone who is not talking or is being very quiet. The crossword solutions for this term are MUM (3 letters), RETICENT (8 letters), and HADOTOSAY (9 letters). MUM means to be silent or not to speak, RETICENT means to be unwilling to talk or express oneself, and HADOTOSAY means to have nothing to say. All three of these words can be used to describe someone who is clammed up.