What is the correct spelling of the expression "lip sync[h]," which refers to miming singing over a recording--usually in a public performance and with the intention to mislead?
Google has approximately 13,700,000 results for "lip-sync," and only ~465,000 for "lip synch" (presumably, it ignores the hyphens). It also suggests "lip sync" as a correction for "lip synch." However, Webster's, Cambridge, and Macmillan give "lip synch" as a headword, and list "lip sync" as a variant or not at all.
What, then, is truly the preferred spelling according to (American-) English convention? I am interested in an answer that makes a compelling argument for one choice or another--informed by knowledge and example of the morphological norms of English, and particularly the rules of clipping--rather than argue that both are acceptable.
Related, but not a duplicate (as it does not treat the fixed phrase with "lip-," but instead other uses of "synch"): "Synced" or "synched"