Comparable to neutrois, there is no one definition of nulltrois, the most common ones are:

• Null-gender / gender-null
• Gender nullity

• Zerogender

• Gender-free / genderfree
• Ambitrois of Negative × Positive
• Mnioct / mniogender
• Voidgender / gendervoid
• Genderhollow / genderempty 

Basically nulltrois was coined to include these identities in the leptrois spectrum (that is neutrois, negatrois, positrois, nulltrois and penultrois). 

The combination of positrois and (th)eir respective negatrois gender(s) can be called negapositrois, zerotrois or posinegatrois, more specifically saying while nulltrois encompasses it all. And the pantrois/omnitrois of negatrois and positrois (pannegatrois×panpositrois or pangender zerotrois) lightrois or infinitrois.

Some nulltrois people may interpret their gender-nullity as xenogender and/or neurogender. ~ ap