It is known that elision means the omission of one or more sounds (such as a vowel (http://en.wikipedia.org/wiki/Vowel), a consonant (http://en.wikipedia.org/wiki/Consonant), or a whole syllable (http://en.wikipedia.org/wiki/Syllable)) in a word or phrase, producing a result that is easier for the speaker to pronounce. Sometimes, sounds may be elided for euphonic effect (http://en.wikipedia.org/wiki/Euphony)
Please I would be grateful if you could tell the difference between assimilation and elision

شكرا لك اخي الكريم

Assimilation is a common phonological (http://www.thanwya.com/wiki/Phonological) process by which the phonetics of a speech segment becomes more like that of another segment in a word (or at a word boundary). A common example of assimilation would be "don't be silly" where the /n/ and /t/ in "don't" are assimilated to /m/ and /p/ by the following /b/, where said naturally in many accents and discourse styles ("dombe silly"). Assimilation can be synchronic (http://www.thanwya.com/wiki/Synchronic_analysis) being an active process in a language at a given point in time or diachronic (http://www.thanwya.com/wiki/Historical_linguistics) being a historical sound change (http://www.thanwya.com/wiki/Sound_change).
A related process is coarticulation (http://www.thanwya.com/wiki/Coarticulation) where one segment influences another to produce an allophonic variation, such as vowels acquiring the feature nasal (http://www.thanwya.com/wiki/Nasal_consonant) before nasal consonants when the velum (http://www.thanwya.com/wiki/Soft_palate) opens prematurely or /b/ becoming labialised as in "boot". This article will describe both processes under the term, assimilation.
المصدر: http://en.wikipedia.org/wiki/Assimilation_(linguistics)