firmness：坚固，坚实；坚定，坚决

词根词缀： -firm-巩固,确定 + -ness名词词尾

• develop
• developed
• developing
• development
• deviant
• deviate
• deviation
• deviationist
• device
• devil
• deviled
• devilishly
• devilment
• devious
• devise
• devoice
• devoid
• devolve
• devote
• devotion
• devour
• devout
• dew
• dexter
• dexterity