stem (n.)

[main body of a tree] Middle English stemme, from Old English stemn, stefn "trunk of a tree or shrub," the part which rises from the ground and supports the branches; also "either end-post of a ship;" from Proto-Germanic *stamniz (source also of Old Saxon stamm, Old Norse stafn "stem of a ship;" Danish stamme, Swedish stam "trunk of a tree;" Old High German stam, German Stamm). This is thought to be from a suffixed form of the PIE root *sta- "to stand, make or be firm."

Especially of the post at the bow of a ship, hence the word came to mean "front of a ship" generally by 1550s. That sense is preserved in the phrase stem to stern, which is originally nautical, "along the full length" (of a ship), and is attested from 1620s.

By 1590s as "stalk which supports the flower of a plant;" the meaning "support of a wineglass" is by 1835. Extended to other things resembling the stem of a plant; in type-founding, "thick stroke of a letter" (1670s); stems as slang for "legs" is by 1860.

The sense of "stock of a family, ancestry" is attested by 1530s; the sense also is in Middle High German stam, Dutch stam; Old High German stam is only in the literal sense, but it meant "race" in compound liut-stam; for which also compare Old English leodstefn "race."

In modern linguistics, the sense of "part of a word that remains unchanged through inflection" is from 1830. In biology, stem cell is attested by 1885.

[hold back the flow of], early 14c., stemmen, "stop, halt, tarry" (intransitive, now obsolete); mid-14c. "stop the flow of, check, dam up" (liquid, speech, etc.); from a Scandinavian source, such as Old Norse stemma "to stop, dam up; be stopped, abate," from Proto-Germanic *stamjan (source also of Swedish stämma, Old Saxon stemmian, Middle Dutch stemon, German stemmen "stop, resist, oppose").

This is considered to be from PIE root *stem- "to strike against something" (source also of Lithuanian stumiu, stumti "thrust, push") and is not considered to be connected to stem (n.). Related: Stemmed; stemming. Also in Middle English as a noun, stemme, "a hindrance."

Phrase stem the tide was originally "hold back the tide" and belongs to this verb but often is confused with stem (v.2) "make headway against."

[make headway against] late 14c., intransitive, "make headway by sailing, head in a certain course," literally "push the stem through," from stem (n.) in the nautical sense of "thick upright beam at the prow of a ship." The transitive sense of "make headway against" is by 1590s; figurative use of this by 1670s. Related: Stemmed; stemming. For stem the tide, see stem (v.1).

in verbal phrase stems from "arises from, has origins in," is by 1932, American English, perhaps from now-obsolete stem (v.) "rise, mount up" (hence "have origin in"), attested from 1570s, from stem (n.). Or it might be influenced by or a translation of German stammen aus "come from," also probably a figurative sense. Compare stem (n.) in the sense of "stock of a family, line of descent." The verb stem meaning "remove the stem of" is by 1873.