The word was first used as a description of yarn or cloth - a sleazy yarn was rough, with projecting fibres and, as a result, sleazy became a general term for thin or flimsy fabric. Sleazy wore badly, picking up dirt and dust because of its poor quality, and it relatively quickly came to apply to anything thin or insubstantial - arguments, for example.
It wasn't until well into this century, though, that the OED first offered evidence of its specifically moral use, to mean squalid 2 or disreputable. The connection is obvious, I guess - morals can be as flimsy as cloth and, in any case, the practice of judging people by the clothes they wear is very ancient (consider the similar case of 'shabby', which refers both to cloth and conduct, and 'shoddy', which derives from a cheap fabric of the same name).
But the logical evolution of the word doesn't tell the whole story about sleazy. It is a good example of how sound alone can carry emotional meaning. In English, for instance, a large number of words beginning with 'sl' are suggestive of dirt or disgust. (Sleazy draws at least some of its current force, I think, from the fact that it combines 'easy' with this particular sound.)
Look through the section of the OED that covers words beginning with 'sl' and you will find, among other things, an astonishing range of words for mud and mire - indeed, the compilers quickly run out of synonyms. It's always said that the Inuit have a large vocabulary for snow, but it seems to be equalled by the lexicon for mud developed by the estuary 3 dwellers and farmers of northern Europe.
You find: sleech (mud deposited by a sea or a river), slabber (street mud, from the German schlabber), sleck (a soft mud or ooze), slaky (muddy), sludge, slime, slip (a very liquid mud, thus slipshod), slew (a muddy pool), slob (an Irish term for sea-shore mud), sloom (soft shale clay), slosh (a watery mud), slub (thick mud), slum (the mud from mine workings), slurry, slush, slop and sludge.
We're moving into murky waters here, but there also seems to be some connection between these ideas (of fluidity and dirt) and a particularly nasty misogyny. Words such as slag, slapper, slut and slattern convey an extra charge of sexual disgust with that opening slur (there is other evidence, too - the archaic word 'sloy', which the OED delicately defines as 'an opprobrious epithet for a woman' and the Dutch word sloor, for a sluttish woman).
Even when the words are not gender specific they are loaded with contempt - slither, sloven, slob, slaver, slum, slouch, slick, slack and slug rarely emerge with good intentions. The association is so strong that it is quite difficult to find approbatory terms that begin with this pair of consonants. Slender has long been approving, as has slim and, to a lesser degree, sleek. Apart from that I can only come up with sloe-eyed, which is cheating slightly.
Onomatopoeia must play some part in this. The way that the tongue smears from the precision of the s into the l gives a sense of the sucking liquidity of mud (the German source words are often even more expressive because they soften the s sound - take schlargen, an old word for smear or mess, which has a real slushy feel to it).
But there's a different type of imitation at work, too - the word forms the mouth into a sneer, drawing back the lip and pulling the tongue away from the bottom of the mouth. Exaggerate it and you get something very similar to your instinctive reaction to a disgusting taste. One recent newspaper report wrote of how the Clintons had got involved with 'a sleazy S&L (savings and loans) operator'. With those initials what else could it have been?
1 From the Greek kanastron, from kanna, reed, via Latin (canistrum, a wicker basket).
2 From the Latin squalere, to be dry, rough, dirty.
3 From the Latin aestus, swell, surge or tide.Reuse content