Synodically

Part of speech: adverb

Definitions

1. Occurring in a way that refers to the duration needed for a celestial body to return to the same position relative to another body
2. Done in a way connected to the interval between successive alignments of celestial bodies
3. Describing an action that corresponds to the time it takes for planets or moons to re-align

Etymology: "Synodically" is an adverb meaning "in planetary cycles," specifically the period between successive conjunctions of two bodies as seen from Earth. Its root, "synod," comes from Late Latin "synodus," which in turn comes from Greek "synodos," meaning "a coming together" or "meeting," built from "syn-" ("together") and "hodos" ("way" or "road"). The idea of two paths meeting in the sky gave astronomers the name for the moment when two planets appear side by side. The adjective "synodical" was formed by adding the suffix "-al" to "synod," and "synodically" comes from adding the adverbial suffix "-ly" to that adjective. Nothing about the history is more complicated than this: the word is a plain English formation built from a Greek root that had already been used for religious assemblies, and it was narrowed to astronomy as a technical term.