1570s, "bottom or foundation" (of something material), from Latin basis "foundation," from Greek basis "a going, a step; a stand, base, that whereon one stands," from bainein "to go, walk, step" (from PIE root *gwa- "to go, come"). The transferred and figurative senses (of immaterial things) are from c. 1600.
c. 1400, reguler, "belonging to or subject to a religious or monastic rule," from Old French reguler "ecclesiastical" (Modern French régulier) and directly from Late Latin regularis "containing rules for guidance," from Latin regula "rule, straight piece of wood" (from PIE root *reg- "move in a straight line"). The classical -a- was restored 16c.
In earliest use, the opposite of secular. Extended from late 16c. to shapes, verbs, etc., that followed predictable, proper, or uniform patterns. From 1590s as "marked or distinguished by steadiness or uniformity in action or practice;" hence, of persons, "pursuing a definite course, observing a universal principle in action or conduct" (c. 1600).
The sense of "normal, conformed or conforming to established customs" is from 1630s. The meaning "orderly, well-behaved" is from 1705. By 1756 as "recurring at repeated or fixed times," especially at short, uniform intervals. The military sense of "properly and permanently organized, constituting part of a standing army" is by 1706. The colloquial meaning "real, genuine, thorough" is from 1821.
Old English borrowed Latin regula and nativized it as regol "rule, regulation, canon, law, standard, pattern;" hence regolsticca "ruler" (instrument); regollic (adj.) "canonical, regular."
c. 1400, reguler, "member of a religious order bound by vows," from regular (adj.) and from Medieval Latin regularis "member of a religious or monastic order." Sense of "soldier of a standing army" is from 1756. Meaning "regular customer" is by 1852; meaning "leaded gasoline" is by 1978; regular (adj.) in the sense of "unleaded" is by 1974.
"in a position above and in contact with; in such a position as to be supported by;" also noting the goal to which some action is or has been directed; "about, concerning, regarding; in a position to cover;" as an adverb, "in or into a position in contact with and supported by the top or upper part of something; in or into place; in place for use or action; into movement or action; in operation," Old English on, unstressed variant of an "in, on, into," from Proto-Germanic *ana "on" (source also of Dutch aan, German an, Gothic ana "on, upon"), from PIE root *an- (1) "on" (source also of Avestan ana "on," Greek ana "on, upon," Latin an-, Old Church Slavonic na, Lithuanian nuo "down from").
Also used in Old English in many places where we now would use in. From 16c.-18c. (and still in northern England dialect) often reduced to o'. Phrase on to "aware" is from 1877.