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Webster 1913 Edition
Alas
A-las′
,int
erj.
 [OE. 
alas
, allas
, OF. alas
, F. hélas
; a 
interj. (L. ah
.) + las 
wretched (that I am), L. lassus 
weary, akin to E. late
. See Late
.] An exclamation expressive of sorrow, pity, or apprehension of evil; – in old writers, sometimes followed by day or white; alas the day, like alack a day, or alas the white. 
Webster 1828 Edition
Alas
ALAS'
,ex.
  An exclamation expressive of sorrow, grief, pity, concern, or apprehension of evil; sometimes followed by day or while; alas the day, like alack a day; or alas the while, expressing an unhappy time.