Reference point
Take a camphor block from an old wardrobe, hold it in your palm and smell.
Do this before you read on. An entry only works when you have just smelled the thing.

Dry, sharp, slightly woody, dusty. It is heavy and closed; it does not open like eucalyptus.
The difference between the two lies in direction: eucalyptus gives a feeling of openness, camphor a feeling of being closed in. The same region of smell but two opposite experiences of space, and this is one of the subtlest pairs in the dictionary.
For many people this smell is inseparable from old wardrobes. The association is so strong that it is hard to separate from the smell itself.
How to smell it
Smell a camphor block in a closed box, then open the lid and smell from a hand’s span away. If there is an old wooden wardrobe at home, open it and smell — that setting gives a thinner version that is easier to analyse.
Why this one is hard
Because memory takes over. Many people smell camphor and report their grandmother’s wardrobe instead of the smell. Both are real, but only one is the goal of the exercise.
Don’t confuse with
This entry
Camphor
Medicinal family
Eucalyptus is airy and clean; camphor is heavy, dry and more closed.
Scientific note
Camphor is a bicyclic ketone that sublimes at room temperature — passing straight from solid to vapour without a liquid stage. Very few substances in this dictionary can do that. That property is what makes a camphor block shrink and disappear completely without leaving any wet mark.
In Vietnamese life
Natural camphor extracted from the camphor tree was once an important commodity in Asia; most commercial camphor today is synthetic. It is a rare case where the synthetic version has almost entirely replaced the natural one without anyone complaining.