Scottish National Dictionary (1700–)
GAB, n.2 In phrs.: 1. the gab o' May, a spell of stormy weather about the beginning of May (n.Sc., Ags., Kcb. 1953); also called the caul' gab (see Cauld, adj., 3.); Marw. (1929) gives the form gaps o' May for Ork.; hence gabach, adj., cold, applied to the weather at this time (Rs. 1911);
2. the gab o' winter, a spell of cold weather in early autumn (Abd.12 1916; Abd.2 1945).
1. ne.Sc. 1881 W. Gregor Folk-Lore 150:
The first days of May . . . were supposed to come accompanied by cold and wet, and hence they were called the “gab o' May.” Abd. 1904 Abd. Weekly Free Press (30 April):
A blast as from the Arctic swept down upon us on Sunday and Monday [24th and 25th April]. . . . People said consolingly that it was the “gab o. May”, but that did not lessen the fact that it was bitterly cold. Abd. 1952 Buchan Observer (6 May):
We have the Gab o' May, or May's cauld kalends to reckon with, and the question comes whether to consume the last of the neeps and straw by keeping the cattle housed instead of turning them out of doors.
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"Gab n.2". Dictionary of the Scots Language. 2004. Scottish Language Dictionaries Ltd. Accessed 13 Dec 2018 <http://www.dsl.ac.uk/entry/snd/gab_n2>
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