You can't restrict to a "word". However, filter criteria operate the same as Edit > Find > Search. So I think you can do the next best thing with leading and trailing spaces, use "match any" with subject contains " ecam" subject contains "ecam " subject is "ecam"

Then I think there are is only one type of situation where a message won't be selected, when ecam is bounded by something other than a space character. Quote character for example.