late 14c., "able to understand, intelligent," from Latin intelligibilis, intellegibilis "that can understand; that can be understood," from intellegere "to understand, come to know" (see intelligence). In Middle English also "to be grasped by the intellect" (rather than the senses). In English, sense of "capable of being understood, that can be understood" first recorded c. 1600. Related: Intelligibly.
Old English leaþr "foam, soap, washing soda," from Proto-Germanic *lauthran (source also of Old Norse lauðr "washing soap, foam"), from PIE *loutro- (source also of Gaulish lautron, Old Irish loathar "bathing tub," Greek louein "to bathe," Latin lavere "to wash"), which is from root *leue- "to wash" + instrumentative suffix *-tro-.
The modern noun might be a 16c. redevelopment from the verb. Meaning "violent perspiration" (especially of horses) is from 1650s; hence the transferred sense "state of agitation" (such as induces sweating), attested from 1839.
also can-can, "A kind of dance performed in low resorts by men and women, who indulge in extravagant postures and lascivious gestures" [Century Dictionary, 1895], 1848, from French, a slang or cant term possibly from can, a French children's word for "duck" (see canard), via some notion of "waddling" too obscure or obscene to attempt to disentangle here. Or perhaps from French cancan (16c.) "noise, disturbance," echoic of quacking.
mid-15c., "hard wafer," but the specific application to a thin, crisp biscuit is by 1739; literally "that which cracks or breaks," agent noun from crack (v.). Meaning "instrument for crushing or cracking" is from 1630s.
Coal-cracker is from 1853 of persons, 1857 of machinery that breaks up mined coal. Cracker-barrel (1861) "barrel full of soda-crackers for sale" was such a common feature of old country stores that the phrase came to be used by 1905 as an adjective, "emblematic of down-home ways and views."
manganese garnet, 1853, earlier spessartine (1837), from French spessartine (1832), from Spessart, district in Bavaria where it is found.
Common garnet generally contains manganese as a component ; which is observable in the colour of the globule that results from melting it with soda. One variety, which contains no lime, has been called spessartine, from its locality, Spessart. ["Conversations on Mineralogy," 1837]