The antonym of 'Decoration' is -

• Decoration (noun)
English Meaning: Something used to make a place or object more attractive or festive, often by adding decorative elements or designs.
Bangla Meaning: সাজসজ্জা; অলংকরণ; শোভা।

Synonym:
Ornament - অলংকরণ; সাজসজ্জা।
Adornment - সাজসজ্জা; শোভা।
Embellishment - শোভাযাত্রা; অলংকরণ।

Antonym:
Plainness - সাধারণতা; সাধনতা।
Simplicity - সরলতা; সাদাসিধা।
Unadorned - অলংকরণহীন; অশোভিত।

Example Sentence:
1. The room's decoration included colourful banners and festive lights for the celebration.
2. She added a beautiful decoration to the cake, making it look even more appealing for the party.

Source:
1. Cambridge Dictionary.
2. Accessible Dictionary by Bangla Academy.