diff --git a/lib/context.js b/lib/context.js
index 2a11055e..98bb02a9 100644
--- a/lib/context.js
+++ b/lib/context.js
@@ -260,6 +260,18 @@ api.createTermDefinition = (activeCtx, localCtx, term, defined) => {
   const mapping = activeCtx.mappings[term] = {};
   mapping.reverse = false;
 
+  // make sure term definition only has expected keywords
+  const validKeys = ['@container', '@id', '@language', '@reverse', '@type'];
+
+  for(let kw in value) {
+    if(!validKeys.includes(kw)) {
+      throw new JsonLdError(
+        'Invalid JSON-LD syntax; a term definition must not contain ' + kw,
+        'jsonld.SyntaxError',
+        {code: 'invalid term definition', context: localCtx});
+    }
+  }
+
   if('@reverse' in value) {
     if('@id' in value) {
       throw new JsonLdError(