I will give you the French definition of the word in all forms. I am French and I consulted the dictionnary to find the right meaning.
Lunatique:
Adjective
1 a) Who is influenced by the moon or certain aspects of the moon (changing,dreamer,naive,crazy,etc...)
b) who is crazy
who is capricious, changing moods....
Substantive
Could be someone who is crazy.


