from The American Heritage® Dictionary of the English Language, 4th Edition
- auxiliary v. Used to indicate ability or permission in the past: I could run faster then. Only men could go to the club in those days.
- auxiliary v. Used with hypothetical or conditional force: If we could help, we would.
- auxiliary v. Used to indicate tentativeness or politeness: I could be wrong. Could you come over here?
from Wiktionary, Creative Commons Attribution/Share-Alike License
- v. Simple past of can.
- v. Used to politely ask for permission to do something.
- v. Used to politely ask for someone else to do something.
- v. Used to show the possibility that something might happen.
- v. Used to suggest something.
from the GNU version of the Collaborative International Dictionary of English
- Was, should be, or would be, able, capable, or susceptible. Used as an auxiliary, in the past tense or in the conditional present.
from The Century Dictionary and Cyclopedia
- n. Preterit of can.
From Middle English coude, from Old English cuþ, preterite form of cunnan ("to be able"). The addition of the silent 'l' was likely a misappropriation attempting to normalize with modal verbs will/would and shall/should. However, while the letter l was historically pronounced in the latter two, can never did have an l sound in it. (Wiktionary)