Morphology is the identification, analysis and description of the structure of words (words as units in the lexicon are the subject matter of lexicology).
In biology morphology is the form, structure and configuration of an organism. This includes aspects of the outward appearance (shape, structure, colour, pattern) as well as the form and structure of the internal parts like bones and organs. This is in contrast to physiology, which deals primarily with function.
Morphology is a branch of life science dealing with the study of gross structure of an organism or taxon and its component parts. It can be subdivided into two distinct branches: anatomy is the study of the structure and internal organs of an organism. The study of the external appearance of an organism is called eidonomy, but while predominant early in the history of biology it is little studied in particular anymore as it is ripe with the effects of convergent evolution. It thus yields less new information about organisms than anatomy, and therefore the external appearance of lifeforms is usually studied as part of general investigations in morphology, e.g. in the context of phylogenetic research.
Also in use is the term "gross morphology", which refers to the prominent or principal aspects of an organism or taxon's morphology. A description of an organism's gross morphology would include, for example, its overall shape, overall colour, main markings etc. but not finer details.
Most taxa differ morphologically from other taxa. Typically, closely related taxa differ much less than more distantly related ones, but there are exceptions to this. Cryptic species are species which look very similar, or perhaps even outwardly identical, but are reproductively isolated. Conversely, sometimes unrelated taxa acquire similar appearance through convergent evolution or even through mimicry. A further problem with relying on morphological data is that what may appear, morphologically speaking, to be two distinct species, may in fact be shown by DNA analysis to be a single species.