Definition/Meaning  Word/Phrase 
sphere of action 
ambit
,
arena
,
compass
,
orb
,
orbit
,
range
,
reach
,
scope

range, sphere, or scope 
ambit
,
orbit
,
radius

point on the celestial sphere toward which the sun and solar system appear to be moving relative to the fixed stars 
apex
,
apex of the sun's way
,
solar apex

freely moving joint in which a sphere on the head of one bone fits into a rounded cavity in the other bone 
articulatio spheroidea
,
ballandsocket joint
,
cotyloid joint
,
enarthrodial joint
,
enarthrosis
,
spheroid joint

sphere of activity, expertise 
bailiwick
,
domain
,
preserve
,
province

early stage of an embryo produced by cleavage of an ovum; a liquidfilled sphere whose wall is composed of a single layer of cells; during this stage (about eight days after fertilization) implantation in the wall of the uterus occurs 
blastodermic vesicle
,
blastula

airfilled sphere 
bubble

small sphere of camphor or naphthalene used to keep moths away from stored clothing 
camphor ball
,
mothball

great circle on the celestial sphere midway between the celestial poles 
celestial equator
,
equinoctial
,
equinoctial circle
,
equinoctial line

great circle on the celestial sphere whose plane passes through the sensible horizon and the center of the Earth 
celestial horizon
,
horizon

(astronomy) the angular distance of a celestial body north or south of the celestial equator; expressed in degrees; used with right ascension to specify positions on the celestial sphere 
celestial latitude
,
dec
,
declination

point in the heavens (on the celestial sphere) 
celestial point

one of two points of intersection of the Earth's axis and the celestial sphere 
celestial pole
,
pole

apparent surface of the imaginary sphere on which celestial bodies appear to be projected 
celestial sphere
,
empyrean
,
firmament
,
heavens
,
sphere
,
vault of heaven
,
welkin

specialized sphere of knowledge 
department

straight line connecting the center of a circle with two points on its perimeter (or the center of a sphere with two points on its surface) 
diameter

sphere of work by women 
distaff

forces at work in a sphere 
dynamics

nonEuclidean geometry that regards space is like a sphere and a line is a great circle 
elliptic geometry
,
Riemannian geometry

circle dividing a sphere or other surface into two usually equal and symmetrical parts 
equator
