A thickener is something you add to a liquid to make it thicker — less runny, more like a sauce or a cream. In the kitchen, the usual ones are cornflour (cornstarch), flour, and egg yolk; in Taiwan we mostly use 太白粉 (potato/tapioca starch) stirred into cold water first. So a thickener is not an ingredient you taste. It is an ingredient that changes how the liquid moves. The word is also used outside cooking, and this is where students meet it in a strange place: on the ingredients list of processed food. Yogurt, ice cream, salad dressing, shampoo, paint, and even some medicines contain thickeners — added not to feed you but to give the product a nicer body, so it does not separate or run off the spoon. On a package you often see it in the plural, or as a label: 'thickener (E1442)'. In that use it sounds technical and slightly industrial, the language of a factory rather than a home kitchen. Grammatically it is a normal countable noun: a thickener, two thickeners, no thickener. It comes straight from the verb 'thicken', so if you know 'the sauce thickened', you already know what the tool for that job is called. Note that the word describes a role, not a substance — the same cornflour is a thickener when you use it to thicken something, and just cornflour when it is sitting in the cupboard.

增稠劑（食品、化妝品標示上的用法）；下廚時我們通常直接說「勾芡用的粉」、「太白粉」。看到包裝成分表寫 thickener，就是增稠劑。