"Wait a minute . . ." (6)
'wait a minute' is the definition.
(thesaurus)
This is the entire clue.
(Other definitions for hold on that I've seen before include "Wait a moment - cling firmly" , "Informally, just a mo', or don't let go" , "Keep one's grasp or maintain telephone contact" , "Cling to - just a second" , "Retain grasp, and don't ring off" .)