ἁψίς
hapsís
“arch, loop”
7 words in English grow from this root.
Apoapsis
Earthἀπόapó
“away from the arch-point”
Apse
Faithἁψίςhapsís
“a joining, a loop”
Apsis
Earthἁψίςhapsís
“a fastening, a loop”
Diapsid
Natureδι-di-
“two arches”
Periapsis
Earthπερίperí
“near the arch-point”
Synapsid
Natureσύνsýn
“arches joined”
Therapsid
Natureθήρthḗr
“beast arch”