IELTS SERIES-8:

IELTS SERIES-8:
IELTsians beware:

DEPARTMENT store OR DEPARTMENTAL store???? 

My wife was on a buying spree. From the mall, I chauffeured her to the always-busy Commercial Street. 
“What is our next destination?” I asked in all politeness though I was irked inside at her shopping mood. I had lost all my 4 hours of reading, watching comedy serials and Face Book.
She looked at me astounded “Don’t you remember even a simple thing? I am telling this 100th time. ‘Go to any Departmental store’ where I would like to purchase some provisions and stationery.”
Driven by this command and to save myself from further salvos for my forgetfulness, I moved the vehicle fast and increased the volume of songs in the car’s stereo.

After a while, I decided that offence is the best form of defense. “I have also told thousand times to you that ‘to say ‘DEPARTMENT STORE” is correct and not ‘DEPARTMENTAL STORE’.” I never miss these unexpected small opportunities to chide her. As usual, she didn't care my words and actually started intently listening to songs. Then, she told “It doesn't matter. After all there are millions who say DEPARTMENTAL STORE.”
“When you go abroad, they may not understand this word-...”
“I won’t go...” is her immediate reply. She opened the door of the car and shut it with a deafening noise. That sound closed my lips from talking further and I followed her gloomily as a person defeated in a fight.

Points to ponder over:
There is no word like ‘DEPARTMENTAL STORE’. (INDIAN usage: OK in India)
IT is ‘DEPARTMENT STORE’ only.
We can say ‘departmental library or departmental action; but NOT DEPARTMENTAL STORE’.
‘DEPARTMENT STORE” is correct.
At least, will you listen to me?