Romo vs. desafilado
In Spanish, both 'romo' and 'desafilado' refer to the state of an item such as a knife or scissors not being sharp. However, they're used in slightly different contexts.
Romo
'Romo' typically refers to an edge or point that was never designed to be sharp, like the end of a stick or the side of a knife.
Este cuchillo es romo, no cortará la carne.
(This knife is blunt, it won't cut the meat.)
El extremo de este palo es romo; no puedes usarlo para atravesar el papel.
(The end of this stick is dull; you can't use it to pierce the paper.)
Desafilado
'Desafilado', on the other hand, implies that an object was once sharp but has lost its edge over time or due to wear and tear.
Mis tijeras están desafiladas, necesitan afilarse.
(My scissors are dull, they need sharpening.)
El cuchillo de cocina está desafilado después de años de uso.
(The kitchen knife is dull after years of use.)
Summary
'Romo' and 'desafilado' both suggest a lack of sharpness but are applied differently. 'Romo' is used for objects that were never meant to be sharp while 'desafilado' applies to items that have lost their sharpness over time.