The definitions of a regular crossword puzzle are exactly the same as the ones you can find in the dictionary - something like I did in the case of the word "sortie", for example, in one of my earlier puzzles. The noun "sortie" is defined by Google as " an attack made by troops coming out from a position of defense," and it is the line I used.
In a more challenging puzzle, we can find definitions which are still accurate but less obvious (or less Googleable). For instance, we will choose to define "sortie" as "a frequent tactic used by the Spanish during the Peninsular War." It was the Spanish war of resistance against the Napoleonic occupation, when the local troops used guerrilla warfare to weaken and eventually defeat the French army.
Keeping this in mind, it is time to go to the next crossword puzzle. Here are the definitions:
ACROSS
1. A mahogany substitute.
2. In principle it generates increased consumption.
3. They produce motion dazzle (singular).
4. A reaction you should totally suppress even if it's hilarious.
5. A component of the International Baccalaureate Diploma Programme core (abbreviation).
6. This is when mad dogs and Englishmen go out.
DOWN
7. They all go when everything is ready (singular).
8. A transition metal that burns in pure nitrogen gas (abbreviation).
9. At peace.
10. Different from the original version.
11. Winner of Super Bowl LII in the 2017 season (abbreviation).
12. A property of matter that can move from one object to another.
As usual, may the force be with you!