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Pergamum
pergola
perhaps
peri
peri-
perianth
periapsis
periapt
periastron
pericarditis
pericardium
pericarp
perichondrium
periclase
periclinal
pericline
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periastron

per·i·as·tron [ pèrree ástrən, pèrree á stròn ] (plural per·i·as·trons)


noun 
Definition:
 
points when stars are nearest: the points in space and time in the orbits of two stars in a binary system at which they are closest together

[Mid-19th century. <peri- + Greek astron "star," after perihelion]
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