I was surprised to find so little dictionary help for this, to me, a common enough word; then it dawned on me that the usual spelling it skosh: you'll see why from the etymology..

skosh
Etymology: < Japanese sukoshi a little, somewhat.
U.S. slang [prob. from the Korean War era - mf]

A little, a small amount; freq. used advb. in the expression a skosh, slightly, somewhat.

[1955 Amer. Speech 30 44 Along with.. everyday greetings, Bamboo English employs sukoshi ‘few, some’ and its antonym takusan ‘plenty’, both of which are forthwith made into two-syllable words, dispensing with the voiceless Japanese u.]

1959 (recorded by Prof. A. L. Hench, Univ. of Virginia) 10 May, ‘Just a skosh,’ he said. When I asked him what he meant he said he had picked the word up in Korea. It means ‘a little bit’. ‘Just a little bit left’ was his meaning.

1977 Detroit Free Press 19 Dec. 4- c/1 In the ad, a slightly out-of-breath jogger laments middle-age body bulge and tells how glad he is that a new line of Levis for men is constructed with ‘a skosh more room where I need it’.

1988 Cycle World Sept. 37/1 The GSX-R's seat is more comfortable than the Yamaha's thinly padded perch, and its bars are a skosh higher.
[OEDonline]