Same as pillar letter-box (which see, under pillar).(noun)
The Century Dictionary (Public Domain)
Use "pillar-box" in a sentence
"Into this frankly pathetic scene comes a ministering angel on a pillar-box red scooter."
"He gives the option of using either plum or round tomatoes – I find the first gives a more watery, less intense flavour, so settle for the pillar-box red cherries I find treading a fine line between ripe and rotten at my nearby Turkish greengrocers."
"It berried early during the warm sunny days of autumn and looked unseasonably odd until surrounding trees dropped their leaves and wintry skies set its clusters of fat pillar-box red berries alight."