Speech and awareness. A simple definition of anomia (inability) or dysnomia (difficulty) is trouble with naming things. This can involve confrontation naming, and sometimes is more evident when being asked to name parts of objects. Agnosia means lack of awareness or knowledge. There are many specific types such as lack of awareness of illness (anosagnosia), lack of ability to recognize faces (prosopagnosia) etc.
All found in AD. Anomia is a problem with word finding and aphasia is a loss of ability to communicate which are all seen in progressive dementia such as Alzheimer's Disease. Aphasia therefore encompasses the anomia.