sabbatarian(n = noun.person) - one who observes Saturday as the Sabbath (as in Judaism);
is a kind of religious person

   sabbatarian(a = adj.pert) - pertaining to the Sabbath and its observance;
Derived form noun sabbath₁

1.  One who regards and keeps the seventh day of the week as holy, agreeably to the letter of the fourth commandment in the Decalogue. [1913 Webster]
" There were Christians in the early church who held this opinion, and certain Christians, esp. the Seventh-day Baptists, hold it now." [1913 Webster]

2.  A strict observer of the Sabbath. [1913 Webster]

   Of or pertaining to the Sabbath, or the tenets of Sabbatarians. [1913 Webster]

sabbatarian, n. & adj.
--n.
1 a strict sabbath-keeping Jew.
2 a Christian who favours observing Sunday strictly as the sabbath.
3 a Christian who observes Saturday as the sabbath.
--adj. relating to or holding the tenets of Sabbatarians.

Derivative:
Sabbatarianism n.

Etymology:
LL sabbatarius f. L sabbatum: see SABBATH

N  impiety, sin, irreverence, profaneness, profanity, profanation, blasphemy, desecration, sacrilege, scoffing, hypocrisy, pietism, cant, pious fraud, lip devotion, lip service, lip reverence, misdevotion, formalism, austerity, sanctimony, sanctimoniousness, pharisaism, precisianism, sabbatism, sabbatarianism, odium theologicum, sacerdotalism, bigotry blue laws, hardening, backsliding, declension, perversion, reprobation, sinner, scoffer, blasphemer, sacrilegist, sabbath breaker, worldling, hypocrite, Tartufe, Mawworm, bigot, saint, Pharisee, sabbatarian, formalist, methodist, puritan, pietist, precisian, religionist, devotee, ranter, fanatic, juramentado, the wicked, the evil, the unjust, the reprobate, sons of men, sons of Belial, the wicked one, children of darkness, impious, irreligious, desecrating, profane, irreverent, sacrilegious, blasphemous, un-hallowed, un-sanctified, un-regenerate, hardened, perverted, reprobate, hypocritical, canting, pietistical, sanctimonious, unctuous, pharisaical, overrighteous, righteous over much, bigoted, fanatical, priest-ridden, under the mask of religion, under the cloak of religion, under the pretense of religion, under the form of religion, under the guise of religion, giovane santo diavolo vecchio.

N  rite, ceremony, ritual, liturgy, ceremonial, ordinance, observance, function, duty, form, formulary, solemnity, sacrament, incantation, service, psalmody, ministration, preaching, preachment, predication, sermon, homily, lecture, discourse, pastoral, baptism, christening, chrism, circumcision, baptismal regeneration, font, confirmation, imposition of hands, laying on of hands, ordination, excommunication, Bar Mitzvah, Bas Mitzvah, Bris, Eucharist, Lord's supper, communion, the sacrament, the holy sacrament, celebration, high celebration, missa cantata, asperges, offertory, introit, consecration, consubstantiation, transubstantiation, real presence, elements, mass, high mass, low mass, dry mass, matrimony, burial, visitation of the sick, seven sacraments, impanation, subpanation, extreme unction, viaticum, invocation of saints, canonization, transfiguration, auricular confession, maceration, flagellation, sackcloth and ashes, penance, telling of beads, processional, thurification, incense, holy water, aspersion, relics, rosary, beads, reliquary, host, cross, rood, crucifix, pax, pyx, agnus Dei, censer, thurible, patera, eileton, Holy Grail, prayer machine, prayer wheel, Sangraal, urceus, ritualism, ceremonialism, sabbatism, sabbatarianism, ritualist, sabbatarian, holyday, feast, fast, Sabbath, Pentecost, Advent, Christmas, Epiphany, Lent, Passion week, Holy week, Easter, Easter Sunday, Whitsuntide, agape, Ascension Day, Candlemas, Ash Wednesday, Good Friday, Holy Thursday, Lammas, Martinmas, Michaelmas, All SAint's DAy, All Souls' Day, Ramadan, Ramazan, Bairam Passover, Shabuoth, Yom Kippur, Day of Atonement, Rosh Hashana, New Year, Hanukkah, Chanukkah, Feast of Lights, Purim, Feast of lots, ritual, ritualistic, ceremonial, baptismal, eucharistical, paschal, what art thou, thou idol ceremony?.

N  asceticism, puritanism, sabbatarianism, cynicism, austerity, total abstinence, nephalism, mortification, maceration, sackcloth and ashes, flagellation, penance, fasting, martyrdom, ascetic, anchoret, anchorite, martyr, Heautontimorumenos, hermit, puritan, sabbatarian, cynic, sanyasi, yogi, ascetic, austere, puritanical, cynical, over-religious, acerbic.