Tooth and nail is an idiom used to describe a strong or fierce effort to do something. Synonyms for tooth and nail include fighting like a tiger, fiercely, vigorously, desperately, zealously, violently, and with all one's might. These synonyms imply that one is putting all of their physical and emotional strength into achieving a goal or winning a battle. The origin of the phrase tooth and nail is often debated, but its meaning has stayed consistent over time. Whether someone is fighting tooth and nail for a promotion, in a legal battle, or for their own personal beliefs, the intensity of their effort is clear.