The initial idioms of the letter A

an itchy palm	an itchy trigger finger
an ivory tower	oceans of
odd fish	off-roader
an offer one can't refuse	oil burner
an old chestnut	old fart
an old flame	an old hand
an old head on young shoulders	an old maid
old salt	an old shoe
an old wives' tale	an/the olive branch
an open book	an open invitation
an open sesame	Oreo cookie
Prevention is better than cure	outside chance
an own goal	an ugly duckling
an Uncle Tom	an unknown quantity
an uphill battle	anaconda mortgage