The verb 'spill' originates from Old English spillan, meaning "to destroy, kill, waste." This sense broadened in Middle English to include "to shed (blood)" and, crucially, "to cause (a liquid) to fall or run out." This semantic shift from general destruction to the specific, accidental loss of liquid is the key evolution. 'Spilt' emerged as a regular past tense and participle form from this root. In modern usage, while both 'spilled' and 'spilt' are correct, 'spilled' is more common in American English, whereas 'spilt' is often found in British English, particularly as an adjective (e.g., "spilt milk").

The word 'spilt' is a variant form of the verb 'spill'. It is not productively formed from separate, meaningful morphemes in modern English. Its core is the Germanic root of 'spill'.