Sandhi

Sandhi (Sanskrit  संधि "joining") is a cover term for a wide variety of phonological processes that occur at morpheme or word boundaries (thus belonging to what is called morphophonology). Examples include the fusion of sounds across word boundaries and the alteration of sounds due to neighboring sounds or due to the grammatical function of adjacent words. Sandhi occurs particularly prominently in Sanskrit phonology, hence its name, but many other languages have it.

As a non-English word, the pronunciation of the word "sandhi" is rather diverse among English speakers. According to Sanskrit phonology it can be pronounced. Acceptable English pronunciations include, ("sandy"), and  among others.

Types of sandhi

 * Internal sandhi features the alteration of sounds within words at morpheme boundaries, as in sympathy (syn- + pathy).
 * External sandhi refers to changes found at word boundaries, such as in the pronunciation for ten books. This is not true of all dialect of English. The Linking R of some dialects of English is a kind of external sandhi, as is the process called liaison in the French language.

While it may be extremely common in speech, sandhi (especially external) is typically ignored in spelling, as is the case in English, with the exception of the distinction between "a" and "an" (sandhi is, however, reflected in the writing system of Sanskrit). External sandhi effects can sometimes become morphologized (i.e. apply only in certain morphological and syntactic environments) and, over time, turn into consonant mutations.

Most tonal languages have tone sandhi, in which the tones of words alter according to pre-determined rules. For example: Mandarin has four tones: a high monotone, a rising tone, a falling-rising tone, and a falling tone. In the common greeting nǐ hǎo, both words in isolation would normally have the falling-rising tone. However, this is difficult to say, so the tone on nǐ is pronounced as ní (but still written nǐ in Hanyu Pinyin).