Pester Unmercifully is a phrase that describes the act of persistently and annoyingly asking someone to do something. The term can be broken down into two words, 'PESTER' and 'Unmercifully'. The 3-letter crossword solution for PESTER is NAG, which is an informal verb meaning to persistently ask someone to do something. Unmercifully means without mercy or compassion, so when combined, PESTER Unmercifully means to persistently ask someone to do something without mercy or compassion.