O

[on a scratched horse]

See: [PUT ONE'S MONEY ON A SCRATCHED HORSE].

[on a shoestring]  {adv. phr.}

With little money to spend; on a very low budget.

[on a volcano]

See: [SIT ON A VOLCANO].

[on behalf of]

See: [IN BEHALF OP].

[on board] (1)  {prep.}

On (a ship).

[on board] (2)  {adv.} or  {adj. phr.}

On a ship.

The captain was not on board when the S.S. Flandre sailed.

[on borrowed time]

See: [LIVE ON BORROWED TIME].

[on call]  {adj. phr.}

1. Having to be paid on demand.

Jim didn't have the money ready even though he knew the bill was on call.

2. Ready and available.

This is Dr. Kent's day to be on call at the hospital.

* /The nurse is on call for  […]

[once]

See:

[AT ONCE],

[EVERY NOW AND THEN] or [EVERY ONCE IN A WHILE].

[once and for all]  {adv. phr.}

1. One time and never again; without any doubt; surely; certainly; definitely.

Let me say, for once and for all, you may not go to the party Saturday.

For once and for all, I will not go swimming with you.

2.  […]