diff --git a/src/cco-modules/ExtendedRelationOntology.ttl b/src/cco-modules/ExtendedRelationOntology.ttl
index 68d6af6..273c5d2 100644
--- a/src/cco-modules/ExtendedRelationOntology.ttl
+++ b/src/cco-modules/ExtendedRelationOntology.ttl
@@ -440,7 +440,7 @@ cco:ont00001861 rdf:type owl:ObjectProperty ;
                  rdfs:domain obo:BFO_0000030 ;
                  rdfs:range obo:BFO_0000030 ;
                  rdfs:label "is material of"@en ;
-                 skos:definition "An object m is material of an object o when m is the material of which o consists and that material does not undergo a change of kind during the creation of o"@en ;
+                 skos:definition "x is_material_of y when both x and y are instances of Object and y consists of x as its material and x undergoes no change of kind during the creation of y."@en ;
                  cco:ont00001760 "https://www.commoncoreontologies.org/ExtendedRelationOntology"^^xsd:anyURI .