not all shared by all lexical categories, include: Nouns hypernyms: Y is a hypernym of X if every X is a (kind of) Y (canine is a hypernym of dog) hyponyms: Y is a hyponym of X if every Y is a (kind of) X (dog is a hyponym of canine) coordinate terms: Y is a coordinate term of X if X and Y share a hypernym (wolf is a coordinate term of dog, and dog is a coordinate term of wolf) meronym: Y is a meronym of X if Y is a part of X (window is a meronym of building) holonym: Y is a holonym of X if X is a part of Y (building is a holonym of window) Verbs hypernym: the verb Y is a hypernym of the verb X if the activity X is a (kind of) Y (to perceive is an hypernym of to listen) troponym: the verb Y is a troponym of the verb X if the activity Y is doing X in some manner (to lisp is a troponym of to talk) entailment: the verb Y is entailed by X if by doing X you must be doing Y (to sleep is entailed by to snore) coordinate terms: those verbs sharing a common hypernym (to lisp and to yell) These semantic relations hold among all members of the linked synsets. Individual synset members (words) can also be connected with lexical relations. For example, (one sense of) the noun "director" is linked to (one sense of) the verb "direct" from which it is derived via a "morphosemantic" link. The morphology functions of the software distributed with the database try to deduce the lemma or stem form of a word from the user's input. Irregular forms are stored in a list, and looking up "ate" will return "eat," for example. Knowledge structure Both nouns and verbs are organized into hierarchies, defined by hypernym or IS A relationships. For instance, one sense of the word dog is found following hypernym hierarchy; the words at the same level represent synset members. Each set of synonyms has a unique index. dog, domestic dog, Canis familiaris canine, canid carnivore placental, placental mammal, eutherian, eutherian mammal mammal vertebrate, craniate chordate animal, animate being, beast, brute, creature, fauna ... At the top level, these hierarchies are organized into 25 beginner "trees" for nouns and 15 for verbs (called lexicographic files