Meaning

noun soft spongelike central cylinder of the stems of most flowering plants

noun the choicest or most essential or most vital part of some idea or experience

verb remove the pith from (a plant)

originThe noun is derived from Middle English pith, pithe (“soft interior; pith, pulp”) [and other forms], from Old English piþa [and other forms], from Proto-Germanic *piþô, from earlier *piþō (oblique *pittan); further etymology unknown. Doublet of pit (“seed or stone inside a fruit”). The verb Middle English pethen (“to give courage or strength”), derived from the noun pith (noun), did not survive…

Etymology from Wiktionary, CC BY-SA 3.0