The inch in inchmeal is the same sort of thing as in the US English inchworm:
photo by Katja Schultz https://www.flickr.com/people/86548370@N00
- that is, a unit of measurement more or less equivalent to two and a half centimetres, or the width of the human thumb (ooh, I've just measured mine, and I have rather slender thumbs) - but the meal bit isn't to do with flakes of grain designed for food use.
No, it's the sort of meal we're supposed to eat three times a day.
Basically, inchmeal is the same sort of word as piecemeal, but instead of something being made or achieved or destroyed piece by piece it happens, yes, inch by inch (an inch being a very small amount).
Ah well. It may be slow, but at least inchmeal means that things are moving in the right direction.
Unless, I suppose, it's the wrong one.
Word To Use Today: inchmeal. The word inch comes from the Old English ynce from the Latin uncia which means a twelfth (though when do you ever see twelve thumbs lined up together? Well, I suppose it might be a good game for breaking the ice at a party). Meal comes from the Old English mælum, a quantity taken at one time.
The English word "inch" (Old English: ynce) was an early borrowing from Latin uncia ("one-twelfth; Roman inch; Roman ounce") not present in other Germanic languages. The vowel change from Latin /u/ to Old English /y/ (which became Modern English /ɪ/) is known as umlaut.