Glum
mid 16th century: related to dialect glum ‘to frown’, variant of gloom.
wiktionary
Probably from Middle Low German glum(“glum”), related to German dialectal glumm(“gloomy, troubled, turbid”). More at gloomy.
From Middle English glomen, glommen, glomben, gloumben(“to frown, look sullen”), from *glom(“gloom”). More at gloom.
etymonline
glum (adj.)
1540s, "sullen, moody, frowning," from Middle English gloumen (v.) "become dark" (c. 1300), later gloumben "look gloomy or sullen" (late 14c.); see gloom. Or from or influenced by Low German glum "gloomy, troubled, turbid." In English the word was also formerly a noun meaning "a sullen look" (1520s). An 18c. extended or colloquial form glump led to the expression the glumps "a fit of sulkiness." Glunch (1719) was a Scottish variant. Related: Glumly; glumness.
