Can grep show only words that match search pattern?

Question

Is there a way to make grep output \"words\" from files that match the search expression?

If I want to find all the instances of, say, \"th\" in a number of files, I

Answer 1

I had a similar problem, looking for grep/pattern regex and the "matched pattern found" as output.

At the end I used egrep (same regex on grep -e or -G didn't give me the same result of egrep) with the option -o

so, I think that could be something similar to (I'm NOT a regex Master) :

egrep -o "the*|this{1}|thoroughly{1}" filename