The initial idioms of the letter A

be joined at the hip	be jolly hockey sticks
be just a pretty face	be just another pretty face
be just the job	be just what the doctor ordered
be keen about	be keen on
be kept in the dark (about something)	be kept on a short leash
be kept on a tight leash	be knee-deep in
be knocked down a peg (or two)	be knocking on heaven's door
be laid to rest	be left hanging (in the air/in midair)
be left (out) in the cold	be left in the dark (about something)
be left in the lurch	be level pegging
be light years away	be light years away from
be light-headed	be like a deer caught in the headlights
be like a dog with a bone	be like a dog with two tails
be like a fish out of water	be like a kid in a candy store
be like a spare prick at a wedding	be like looking for a needle in a haystack