could

Multiple Entries:
  could    can  

Concise Oxford English Dictionary © 2008 Oxford University Press:
could/kəd/

▶modal verb past of can1.

■ used in making suggestions or polite requests: could I use the phone?

usage: For a discussion on the use of could of instead of could have, see usage at have.

Concise Oxford English Dictionary © 2008 Oxford University Press:
can1

▶modal verb (3rd sing. present can; past could)

• 1 be able to.

  ■ [with neg. or in questions] used to express doubt or surprise: he can't have finished.

  ■ used to indicate that something is typically the case: he could be very moody.

• 2 be permitted to.

– origin OE cunnan ‘know’.

usage: The use of can rather than may to request or express permission, as in may/can I ask you a few questions?, is not incorrect in standard English, although some people object to it. May is, generally speaking, a more polite way of asking for something, however, and is the better choice in more formal contexts.

Concise Oxford English Dictionary © 2008 Oxford University Press:
can2

▶noun

• 1 a cylindrical metal container, in particular one in which food or drink is hermetically sealed for storage over long periods.

• 2 (the can) N. Amer. informal prison.

• 3 (the can) N. Amer. informal a toilet.

• 4 (cans) informal headphones.

▶verb (cans, canning, canned)

• 1 preserve in a can.

• 2 N. Amer. informal dismiss from a job or reject as inadequate.

– phrases
a can of worms a complicated matter likely to prove awkward or embarrassing.
in the can informal on tape or film and ready to be broadcast or released.

– derivatives
canner noun.

– origin OE canne, either of Gmc origin or from late L. canna.