Orphaned word stems
Certain words in the English language are only defined with prefixes attached to them, but not by themselves. The example that got me thinking of this, which I've heard used in really poor standup comedy routines, is whelm, which seems to only exist as part of the words "overwhelm" and "underwhelm." Surprisingly, this is not a true example, "whelm" is actually a a word, so I listed in the non-examples section. Nevertheless, I've found a few true examples. I think they can only count if the etymology of the word shows that exists in English as a root plus one more normal prefixes.
||deflect, inflect, reflect
||congress, egress, ingress, progress, regress
||expect, inspect, introsprect, prospect, respect, retrospect
||helmian (Old English)