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Ok, then, I think the answer to this conundrum could be Custom.

Clip, fold and dust are all concrete nouns in so far as they are actual things which you can see and touch - a paper or hair clip, for instance and a fold is either a doubling over of paper or fabric, for example, or a fold is a sheep enclosure. You can sweep dust under the carpet (if you're not fussy about cleanliness, or your vacuum cleaner is broken).

Custom is an abstract noun - it is a concept or idea; it is a tradition or procedure.