"He is always machmir to brush his hat and straighten his tie before he goes out in public." (Weiser)

"When there is a doubt in a matter of Torah law, you must be machmir (strict); when there is a doubt in a matter of rabbinic law, you may be makil (lenient)." (source)

"Some of the rabbis aren't prepared to recognize the Ethiopian Jews, but perhaps they're being machmir about it." (Glinert)