the commencement of two or more stressed syllables of a word group either with the same consonant sound or sound group (consonantal alliteration) as in from stem to stern, or with a vowel sound that may differ from syllable to syllable (vocalic alliteration) as in each to all.
British Dictionary definitions for consonantal all iteration
the use of the same consonant (consonantal alliteration) or of a vowel, not necessarily the same vowel (vocalic alliteration), at the beginning of each word or each stressed syllable in a line of verse, as in around the rock the ragged rascal ran
C17: from Medieval Latin alliterātiō (from Latin al- (see ad-) + litera letter), on the model of obliterātiōobliteration
Word Origin and History for consonantal all iteration
1650s, "to begin with the same letter," from Mod.L. alliterationem (nom. alliteratio) from alliteratus, pp. of alliterare "to begin with the same letter," from L. ad- "to" + littera (also litera) "letter, script" (see letter). Formed on model of obliteration, etc.