blank canvas

A person or thing that has nothing of substance or permanence within or imprinted upon him, her, or it, such that it can be easily filled with entirely new things. Refers to a painter's canvas that has yet to be painted on. Children's minds are blank canvasses, so we have to be sure to provide them with enriching education and opportunities so as to give them the best possible future. I love moving into a new house and having a blank canvas to make my own! These freshmen are all blank canvasses—we can get them to believe anything we tell them!

by a canvas

By an extremely short or slim margin (of distance, time, or another measure). The phrase comes from boat racing, as the front end of a racing boat was at one time covered with canvas. They're just about to close the gates! It looks like we made the flight by a canvas. The race was neck and neck till the very end, but Sally won it by a canvas. Ah, she lost the gold medal by a canvas when her leg cramped in the last few meters.

under canvas

Under or within a tent. There are dozens of vendors who sell their goods under canvas at our market each Saturday.

by a canvas

by a small margin.

The tapered front end of a racing boat was formerly covered with canvas to prevent water being taken on board. In this context, to win by a canvas meant to win by the length between the tip of the bow and the first oarsman.

under canvas

1. Nautical With sails spread.

2. In a tent or tents.