The word is found in Scotland, where Ferguson's 1641 book of proverbs had 'A toom purse makes a blate [bashful, timid] merchant.' Hence half-toom, half empty, toom-full, full to running over, toom-brained, empty-headed, and the phrases found both in Ulster and scotland, as toom as a whistle, and as toom as an egg-shell, entirely empty. Burns has 'Her mutchkin [a Scots liquid measure, about three quarters of an imperial pint] stoup [a pitcher] as toom's a whissle,' in his poem Earnest Cry.Toom is also used of vain, empty-sounding words. Burns, in Kirk's Alarm, has 'Ye hae made but toom roose [rough noise]!'Then there is the verb toom, which means to empty; to pour out; to draw off water from anything boiling. The Ballymena Observer of 1882 has 'Toom the potatoes; toom them up.' The verb in this meaning is still used in Co Antrim. Hence toomed, swayed on one side, as in pouring water from a bucket; of a woman, delivered of a child; toom the stoup, noun, a drunk.
This is a variant of the verb teem, which means 'to empty' and also of rain, 'to pour down in torrents'. The Dictionary of the Scots Language gives an 1880 Ulster example of the word as, a noun, meaning 'a downpour' - 'I was out in a perfect teem'.