Phonology . the change of a pure vowel to a diphthong, esp. in certain environments, as, in Old English, the change of a vowel to a diphthong under the influence of a following consonant or combination of consonants, as the change of -a- to -ea- and of -e- to -eo- before preconsonantal r or l and before h, as in earm arm developed from arm, and eorthe earth from erthe.

adjective

enduring , strong

noun

union

adjective

splitting , cracking , shattering , splintering , fracturing , tearing , smashing , crumbling , collapsing

noun

separation , detaching , detachment , dividing , parting , partition