consider

The oldest reading of consider is an astronomical one. Latin considerare parses, on the face of it, as con-, "with, together," and sidus, "star, constellation" — and the literal sense would then be "to observe the stars." Two pictures have been offered for why thinking-a-thing-over should be named after star-watching. One is navigation: the careful person reads the sky the way a steersman reads it, to fix where they are and where to go. The other is augury: in a Rome obsessed with divination, you read the heavens — the flight of birds, the look of the constellations — before any consequential action was permitted to proceed. On either picture, to consider is to look up at something you did not make and read it for instruction.

It is a lovely etymology and an honest entry has to say plainly how unsettled it is. Etymonline gives "probably literally to observe the stars" and then immediately records that de Vaan — the standard modern authority on Latin — "considers various alternative etymologies for the Latin verb but endorses none." A century ago, Tucker doubted the star-derivation and traced the word instead to the root of English side, meaning "stretch, extend" — giving the whole verb, on his reading, the sense "to survey on all sides, to dwell long upon." And even if you accept that -sider- is sidus, the trail goes cold one step down, because sidus itself has no agreed origin: the reconstructions on offer point at "sweat," at "achieve a goal," at a non-Indo-European borrowing, at "binding." So the star-story sits on two uncertainties stacked — is the -sider- really a star, and where does the star come from — and the right posture toward it is the one the word itself recommends: hold it, weigh it, do not commit.

The one place the star-root is not in doubt is sidereal — "of the stars," the astronomer's adjective, from sidus plainly and uncontroversially. And the place the uncertainty matters most is desire, which is the same hypothesis run on a different prefix: de sidere, "from the stars." Consider and desire are a matched pair — to read the stars, and to long for what they will or will not give — and they stand or fall together, because they rest on the same contested claim about sidus. If the star-etymology is right, they are the two halves of a single ancient gesture toward the night sky: attention and want. If it is wrong, they are two ordinary Latin verbs that happen to rhyme. The honest answer is that we do not know, and the not-knowing is itself in the spirit of the word.

The false friends are the other -sid- words, which look like kin and are not. Preside, reside, president, sediment, sedentary all carry not sidus ("star") but sedēre ("to sit"): a president "sits in front," a resident "sits back." Different root entirely, the ordinary PIE *sed-, "to sit." Cider is closer to pure coincidence — a Semitic loanword, Hebrew shekhar, "strong drink," wearing a Latin sic- spelling. And the con- is no help in sorting them, because console and consul share the prefix and carry entirely different second halves. Only the stars, if they are stars at all, tie consider to desire. It is fitting that a word for careful judgment should turn out to be a word whose own judgment is suspended — a question still under consideration.