What would this unsaturated cyclic compound be called?
Chemspider tells me that the name should be


  1,1'-Bi(cyclohexylidene)


http://www.chemspider.com/Chemical-Structure.121798.html?rid=e40cd595-d5e5-450e-bdb3-3e558a9da92d

While PubChem mentions:


  Cyclohexylidenecyclohexane


https://pubchem.ncbi.nlm.nih.gov/compound/Cyclohexylidenecyclohexane




  My guess was maybe it's "cyclohexylene cyclohexane"


There's a flaw to this thinking, to name this, I'd suggest you choose one of the cyclohexane rings to act as the word-root. Now you've to just add the name of the substituent.

Recall that (source: http://www.ebi.ac.uk/chebi/searchId.do?chebiId=65236) also click this link for an example (this website particularly has propylidene group as the example):


  An alkylidiene group formed from propane by removal of two hydrogen atoms from the same carbon atom, the free valencies of which are part of a double bond.


So, the substituent in this case would be called "cyclohexyl idene " (without the space). And hence, the name should be cyclohexylidenecyclohexane.