It means to be overwhelmed, to be defeated. Shellacking is a slang term meaning to be defeated hollow.
“The “e” in the first syllable is like the “a” in “china”, and the remaining two syllables are pronounced like the word “lacking”. The main stress is on the second syllable.
The word “shellacking” can also be used to mean to beat someone physically.
* When the manager caught the young boy stealing, he gave him a good shellacking. * If I don’t return home in 20 minutes I’ll get a good shellacking.*The Wimbledon champion took a shellacking from the unseeded opponent.