egrep -i “^s[a-z]{0,1}m[a-z]{0,1}b[a-z]{0,1}$” /usr/share/dict/words just gives you less results than other commands

Many possibilities

egrep -i “^s.*m.*b” /usr/share/dict/words

.* means any character (.) for as many times (*) before encountering m or b, as the case may be.

So, search for words beginning with “s” with any number of additional letters, then an “m”, any additional letters and a “b”