Etymology Irregular form of heat up. The adjective was originally a metaphorical use of the past participle het up (“heated up”), perhaps as a reference to agitation caused by fever or the churn of boiling water, but has since lexicalised as a fossil in standard English.
"I reckon," he said, directing his remarks toward no one in particular, "that we've all been rather hasty in this matter, being het up as we were with the strain of what we been through an' so it seems to me, […]1914 October – 1916 July, Edgar Rice Burroughs, The Mucker, Chicago, Ill.: A[lexander] C[aldwell] McClurg & Co., published 31 October 1921, →OCLC:
2 more examples
‘What ever happened ashore to get that cold old turtle so het up?’ he demanded.1932, Delos W. Lovelace, King Kong, published 1965, page 62:
We must do an end run around these people, not make the mistake of thinking they are just “het up” or have wended a few yards into a wrong turn.2021, John H. McWhorter, chapter 6, in Woke Racism, New York: Forum, →ISBN: