Definition -
(1) The transition between two linguistic segments.
(2) The transition between an utterance and the preceding or following silence.

Example -
In modern English there is no juncture between the an and the other in the word another, but formerly there was, thus the concept was expressed as the two-word phrase an other.

Oxford English Dictionary -
The term's first citation is from 1934:
"When a stem-vowel or declensional suffix in its crude form occurs in the first components of compound substantives and adjectives, it is called the ‘Fugenvokal’, i.e. juncture vowel.
(Priebsch & Collinson German Lang. iii. 210)

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