President Obama described the defeat his party suffered in the recent mid-term elections as a 'shellacking'. Shellacking as a noun is in the Oxford English Dictionary (OED), but not in the shorter Oxford Dictionary of English (ODE), nor in Collins. The word dates back to the 1930s and the OED says it is "chiefly US". The definition, apart from the literal 'a coating of shellac' is 'a beating or thrashing, a pasting, or a defeat'. The word comes from the noun shellac, a lac resin used as a varnish and formerly used in the manufacture of gramophone records.
There aren't many verbs ending in the letter C in English (the commonest are picnic, bivouac, panic, mimic, frolic and tarmac), but the general pattern is for a K to creep in before a suffix beginning with a vowel: panicked, mimicking, picknicker. There is usually no K if the suffix begins with a consonant: frolicsome, trafficless. Nor is there usually a K in the third person singular form of the present tense: mimics, picnics, frolics, tarmacs. In Collins Dictionary the verb to shellac follows this pattern (shellacs), but the ODE has shellacks. The OED doesn't give any form (although it has an 19th-century citation where 'shellacing' is written without a k). Inflected forms from the verb 'to arc' don't usually add a K either (arcing, arced). You would write lip-synced or lip-synched, but not lip-syncked, -nck- not being a usual English combination of letters.