The phrase "in appreciable" generally refers to something that is small or insignificant, but there are a number of synonyms that can be used in its place. One option is "negligible," which suggests that something is so small as to not even be worth considering. Another possibility is "insignificant," which implies that a particular amount or effect is too small to make any real difference. "Minimal" is another good synonym, as it underscores the fact that something is very small, but may still have some measurable impact. Finally, "inconsequential" can be used to describe something that is so small as to be virtually meaningless.