Words related to *gembh-
1777, "a projecting part of a rotating machinery used to impart motion to another part," from Dutch cam "cog of a wheel," originally "comb," from Proto-Germanic *kambaz "comb," from PIE root *gembh- "tooth, nail." It is thus a cognate of English comb (n.). This might have combined with English camber "having a slight arch;" or the whole thing could be from camber.
It converts regular rotary motion into irregular, fast-and-slow rotary or reciprocal motion. "The original method was by cogs or teeth fixed or cut at certain points in the circumference or disc of a wheel ..." [OED]. Cam-shaft attested from 1850.
Old English camb (later Anglian comb) "thin strip of toothed, stiff material" (for dressing the hair), also "fleshy crest growing on the head of the domestic fowl" (so called for its serrations), hence "crest of a hat, helmet, etc.;" also "honeycomb" (for which see honeycomb (n.)) , from Proto-Germanic *kambaz (source also of Old Saxon and Old High German camb, German Kamm, Middle Dutch cam, Dutch kam, Old Norse kambr), literally "toothed object," from PIE *gombhos, from root *gembh- "tooth, nail."
From c. 1300 as a tool for carding wool (probably earlier; Comber as a surname is from c. 1200). Comb-paper (1866) is marbled paper in which the design is produced mostly by use of a comb.
"a precious stone" (especially when cut or polished), c. 1300, probably from Old French gemme (12c.), from Latin gemma "precious stone, jewel," originally "bud," from Proto-Italic *gebma- "bud, sprout," from PIE *geb-m- "sprout, bud" (source also of Lithuanian žembėti "to germinate, sprout," Old Church Slavonic prozebnoti "to germinate").
The two competing traditional etymologies trace it either to the root *gembh- "tooth, nail" [Watkins] or *gem- "'to press." De Vaan finds the second "semantically unconvincing" and leans toward the first despite the difficult sense connection.
Of persons, "a rare or excellent example (of something)" from late 13c. Alternative forms iemme, gimme persisted into 14c. and might represent a survival of Old English gimm "precious stone, gem, jewel," also "eye," which was borrowed directly from Latin gemma.
"coarse, loose fiber obtained from taking apart old hemp ropes," used for caulking the seams of wooden ships, etc., early 15c., okam, okum, from Old English acumba "tow, oakum, flax fibers separated by combing," literally "what is combed out," from Proto-Germanic *us-kambon (source of Old High German achambi). The first element is cognate with Old English a- "away, out, off;" the second element is from stem of cemban "to comb," from camb "a comb;" from PIE root *gembh- "tooth, nail."
1570s, from un- (1) "not" + kempt "well-combed, neat," from variant past participle of Middle English kemben "to comb," from Old English cemban "to comb," from Proto-Germanic *kambijan, from *kamb- "comb" (from PIE root *gembh- "tooth, nail." ). Form unkembed is recorded from late 14c. The verb kemb is rare after 1400s, but its negative past participle form endures.