Origin and history of richly

Old English rice "strong, powerful; great, mighty; of high rank" (senses now obsolete), in later Old English "wealthy;" from Proto-Germanic *rikijaz (source also of Old Norse rikr, Swedish rik, Danish rig, Old Frisian rike "wealthy, mighty," Dutch rijk, Old High German rihhi "ruler, powerful, rich," German reich "rich," Gothic reiks "ruler, powerful, rich"), borrowed from a Celtic source akin to Gaulish *rix, Old Irish ri (genitive rig) "king," from Proto-Celtic *rix, from PIE root *reg- "move in a straight line," with derivatives meaning "to direct in a straight line," thus "to lead, rule" (compare rex).

The form of the word was influenced in Middle English by Old French riche "wealthy, magnificent, sumptuous," which is, with Spanish rico, Italian ricco, from Frankish *riki "powerful," or some other cognate Germanic word. Old English also had a noun, rice "rule, reign, power, might; authority; empire" (compare Reich). The evolution of the word reflects a connection between wealth and power in the ancient world, though the "power" sense seems to be the oldest.

In transferred and extended senses from c. 1200. The meaning "magnificent" is from c. 1200; that of "of great value or worth" is from mid-13c. Of food and colors, "having an abundance of a characteristic quality that pleases the senses," from early 14c.; of sounds, from 1590s; of soils from 1570s. Sense of "entertaining, amusing" is recorded from 1760. The noun meaning "the wealthy" was in Old English.

English once had a related verb rixle "have domination, rule," from Old English rixian "to rule."

common adverbial suffix, forming, from adjectives, adverbs signifying "in a manner denoted by" the adjective; Middle English -li, from Old English -lice, from Proto-Germanic *-liko- (source also of Old Frisian -like, Old Saxon -liko, Dutch -lijk, Old High German -licho, German -lich, Old Norse -liga, Gothic -leiko). See -ly (1). It is 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.