meticulously adv.

1530s, "fearful, timid," a sense now obsolete, from Latin meticulosus, metuculosus "fearful, timid," literally "full of fear," from metus "fear, dread, apprehension, anxiety," a word of unknown origin. The old word seems to have become archaic after c. 1700, fossilized in a passage of Sir Thomas Browne, though it turns up occasionally and obscurely as late as 1807.

It began to return to English in a sense of "fussy about details" by 1840s, from French méticuleux "timorously fussy" [Fowler, who rails against it, attributes this use in English to "literary critics"], the French descendant of the Latin word, but it took time for this to percolate. Meticulous appears 1852 in Halliwell's "Dictionary of Archaic and Provincial Words" (with the definition "timorous") and is marked "obsolete" in Craig's dictionary of the same year. It was listed by Richard Trench ["English Past and Present," 1868], who started the movement that became the OED,  among the words that had been "rejected and disallowed by the true linguistic instincts of the national mind."

It is marked archaic in the Imperial Dictionary (1883), which has only the sense "timid," but not so marked in Century Dictionary (1890), which defines it as "Timid; over-careful." It was much criticized, and somewhat defended, in writerly publications c. 1914-1924. Related: Meticulosity.

common adverbial suffix, forming from adjectives adverbs signifying "in a manner denoted by" the adjective, Middle English, from Old English -lice, from Proto-Germanic *-liko- (cognates: Old Frisian -like, Old Saxon -liko, Dutch -lijk, Old High German -licho, German -lich, Old Norse -liga, Gothic -leiko); see -ly (1). Cognate with lich, and identical with like (adj.).

Weekley notes as "curious" that Germanic uses a word essentially meaning "body" for the adverbial formation, while Romanic uses one meaning "mind" (as in French constamment from Latin constanti mente). The modern English form emerged in late Middle English, probably from influence of Old Norse -liga.