(n. pl.) foolish or moody doubts or misgivings, or reasons for not doing something [18thC dial.]
When you start offering silly excuses for not doing something, or your brain is full of flawed doubts or misgivings, those are antherums.
Antherums is a dialect word pinpointed to the dialects of Yorkshire, Derbyshire, and North Country English specifically by the English Dialect Dictionary. The EDD also records a wealth of alternative spellings, like antrims, antrums and tantrums.
It is the last of these that likely gives us some clue as to this word’s origin. A tantrum is of course a fit of ill temper, and that word has been used as such in English since the early eighteenth century. For such a familiar word, oddly tantrum is a complete mystery: it emerged seemingly out of nowhere in the early 1700s in the form tanterum, before steadily streamlining to the clipped form we have today. It’s possible there may be some kind of distant link to one of the languages of central Asia—tantiram, for instance, is a Tamil word for a ploy or trick—so it may well be that this is a word word commandeered into English during the establishment of the Indian trade roots that would eventually form the basis of the British Raj during the Victorian era. But without much further evidence to go on, the word remains something of a mystery.
Whatever it’s origins may be, it seems likely that people’s moody tantrums are the origin of our anthrums, or antrims: as the English Dialect Dictionary also points out, as well as meaning doubts or hesitations, anthrums can also be used of “airs, whims, caprices, with an implication of temper.”