abeo

Abeo, abire, abii, abitum is ab plus eo, and it inherits the parent verb's whole irregular conjugation: abeo, abis, abit, abimus, abitis, abeunt, imperfect abibam, future abibo. The perfect abii is contracted from abivi.

That contraction sets the trap this corpus keeps springing. Abit is present, "he goes away"; abiit is perfect, "he went away". One letter, two tenses, and no other signal in the word itself. Beyond physical departure, abeo does time passing (dies abiit) and one thing turning into another - in vanum abire, "to come to nothing", abire in saxum, "to turn to stone". The imperative abi is blunt, closer to "clear off" than to "please leave".