A morpheme is often described as the smallest unit of meaning in a word. This suggests that there are two morphemes in the word pancake, namely, pan and cake, both of which have rather obvious, recognizable meanings, and both of which are words by themselves. The adjective pink is different from the suffix -ish; pink is a free morpheme but -ish is a bound morpheme, one which must be attached to another root or word. Words can be monomorphemic, or made up of a single morpheme, or they can be polymorphemic, made up of combinations of morphemes, including affixes, such as suffixes and prefixes. Inflectional affixes do not change the category of the word they attach to, nor do they create new dictionary entries. Word trees allow to express yet another aspect of morphology, namely that inflectional affixes always occur outside of derivational affixes. Word trees also helps to understand the different meanings of a word or lexical ambiguity.