Here are three sets of similar words all starting with D that have different meanings from their near doubles.
DEFINITE and DEFINITIVE: Definite means specific, precise.
The driving teacher gave definite instructions about what her student should expect on the road test.
Definitive means conclusive, final. The algebra problem, complicated as it was, had a definitive solution that few students were able to reach.
DEFUSE and DIFFUSE: Defuse means to make a situation less harmful. The crowd was getting agitated, but the master of ceremonies’ good nature was able to defuse the nerves of the people in the audience.
Diffuse means to disperse or disseminate, to spread over a wide area. The natural gas that had been escaping for months is now more diffuse so that residents can return to their homes.
DISASSEMBLE and DISSEMBLE: Disassemble means to take apart. When she was only six years old, Katie disassembled the clock to see how it worked.
Dissemble means to conceal, perhaps to lie. Katie dissembled about taking the clock apart when her parents found the parts strewn across the floor of her room.