Full Idea
Not only material bodies but also properties, relations, events, numbers, sets, and propositions are—if they are acknowledged as existing—to be accounted ‘things’.
Gist of Idea
Bodies, properties, relations, events, numbers, sets and propositions are 'things' if they exist
Source
E.J. Lowe (Things [1995])
Book Reference
'Oxford Companion to Philosophy', ed/tr. Honderich,Ted [OUP 1995], p.871
A Reaction
There might be lots of borderline cases here. Is the sky a thing? Is air a thing? How is transparency a thing? Is minus-one a thing? Is an incomplete proposition a thing? Etc.