How does one form composites from words in '-σις'? For example, if one wishes to name the fear of vaxing fat, using πάχυνσις, is it παχυνσοφοβία; or παχυνσεοφοβία?
My expectation would be that the base stem would be used, thus παχυνσιφοβία. I haven't found a lot of examples to support this, but there is, for example, πραξι‐κοπεῖν "to take by surprise" from πρᾶξις and στασι‐ωρός "watcher of the station" from στάσις.
P.S. What's "vaxing fat"?