The phenomenon in Arabic
of having a hamza
(a glottal stop
) at the beginning of word when spoken in isolation, but eliding
it when it is preceded by another word ending in a vowel
. Arabic words can't actually begin with a vowel. Those that do tack a glottal stop in front. But in elision
with a preceding vowel, both this hamza and the initial vowel are omitted.
Example, "the house" is al-bayt, and "in" is bi. Said in isolation or at the beginning of a sentence, "the house" is pronounced ?al-bayt, where "?" represents the hamza or glottal stop. But when combined with bi, it forms the connected phrase bi-l-bayt, where the A of the article al- "the" is also omitted.
This temporary hamza is the hamzatulwasl. That name is itself an example, since it combines hamzah and al-wasl. But to explain how A and AH and ATU are connected takes us into the somewhat complicated phenomenon of ta marbuta q.v.
Not all initial hamzas are elided; some are permanent, as in bi ?ayyi bayt 'in any house'.
The S is wasl is the emphatic letter sad, so it's pronounced wosl.