Old English cuðe, past tense of cunnan "to be able" (see can (v.1)); ending changed 14c. to standard English -d(e). The unetymological -l- was added 15c.-16c. on model of would, should, where it is historical. Could be as a response to a suggestion, indicating it may be correct, is by 1938.

also counter-intuitive, "contrary to intuition, opposed to what would be expected," 1955, from counter- + intuitive.

"a would-be philosopher," a disparaging term for a rationalist or skeptic, a philosophe; 1798, from French philosophiste; see philosophy + -ist.

"amorous or designing widow," 1907, from the English title of Franz Lehar's operetta "Die Lustige Witwe" (1905). "The Lusty Widow" would have been more etymological (see lust (n.)), but would have given the wrong impression in English. Meaning "a type of wide-brimmed hat" (popularized in the play) is attested from 1908.