Notmuch doesn't support regular expressions ("wildcards") when searching the body of messages, see the man page  for `notmuch-search-terms`. It computes stems of words and indexes (and searches) those.

Using xapian commands, one could extract all stems and grep those for a term which one "remembers partially" (often happened to me), and then feed that into notmuch. Might be worthwhile scripting or even integrating into notmuch (sexp?).

Michael