"expel saliva," Old English spittan (Anglian), spætan (West Saxon), transitive and intransitive, past tense *spytte, from Proto-Germanic *spitjan, from PIE *sp(y)eu-, of imitative origin (see spew (v.)). Not the usual Old English word for this; spætlan (see spittle) and spiwan are more common; all are from the same root. To spit as a gesture of contempt (especially at someone) is in Old English. Related: Spat; spitting.
"saliva," early 14c., from spit (v.1). Meaning "the very likeness" in modern use is attested from 1825 (as in spitting image, attested from 1887); compare French craché in same sense. Spit-curl (1831) was originally considered colloquial or vulgar. Military phrase spit and polish first recorded 1895.
"sharp-pointed rod for roasting meat," late Old English spitu "a spit," from Proto-Germanic *spituz (source also of Middle Dutch and Dutch spit, Swedish spett (which perhaps is from Low German), Old High German spiz, German Spieß "roasting spit," German spitz "pointed"), from PIE *spei- "sharp point" (see spike (n.1)). This is also the source of the word meaning "sandy point" (1670s). Old French espois, Spanish espeto "spit" are Germanic loan-words. The verb meaning "to put on a spit" is recorded from c. 1200.
c. 1200, "put on a spit, thrust with a spit," from late Old English sputtian "to spit" (for cooking), from spit (n.2). Meaning "pierce with a weapon, transfix, impale" is from early 15c. Related: Spitted; spitting. Nares' Glossary has spit-frog "a small sword."