Scottish National Dictionary (1700–)
-UM, suff. Also -im, -om, -am, -em, and in pl. forms with -s, esp. in children's language. [-əm]
1. Added to noun or verb stems to form nouns with dim. or hypocoristic force, as in Breekums, brinkum s.v. Brinkie, Didderums, Doldrum, Fegrim, Ginkum, Groatum, Keekum, Leggums, Nickum, quirklum s.v. Quirk, scoudrum s.v. Scowder, etc. Cf. colloq. or childish Eng. diddums.
2. Used to form advs. as in legim, astride, s.v. Leg. Rare.[A formation, prob. orig. jocular, based in 1. on Lat. -um, neuter ending of -o- stems, partly an altered form of -in(g)s, vbl.n. ending, in 2. on O.E. -um, adv. ending, as in Whilom.]
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"-um suffix". Dictionary of the Scots Language. 2004. Scottish Language Dictionaries Ltd. Accessed 12 Aug 2020 <https://www.dsl.ac.uk/entry/snd/um>
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