vagary

noun

1. An erratic, unpredictable occurrence or action.

   “It now turns out that the Pitch Lake, like most other things, owes its appearance on the surface to no convulsion or vagary at all, but to a most slow, orderly, and respectable process of nature, by which buried vegetable matter, which would have become peat, and finally brown coal, in a temperate climate, becomes, under the hot tropic soil, asphalt and oil, continually oozing up beneath the pressure of the strata above it.”

   “This searching was facilitated by the author's knowledge of the vagaries of Anglo-Indian spelling and the numerous colonial-era transliteration systems used for loanwords from Indian languages.”

   “These systems learn the vagaries of language by analyzing enormous amounts of text, including thousands of books, Wikipedia entries and other online documents.”

2. Something vague.

   “to speak in vagaries”

3. An impulsive or illogical desire; a caprice or whim.

   “And then came the day when my socialism grew respectable,—still a vagary of youth, it was held, but romantically respectable.”