sub

• subject, subsidize, substitute, substance
• substantial, submit, subsist, subsidiary, subscription, subscribe, subside, subdue, subvert

prefix sub- (under, below, less than):
substandard, subpar, subtract, subtitle, subhead, subheading, subheadline, subparagraph, subtext, subsequent, submarine, submerge, subconscious, subliminal, subdivide, subcommittee, subgroup, subclass, subdomain, subnet, subset, subarray, subsection, subcategory, subfolder, submenu, subcontract, subcomponent, sublet, sublease, subfloor, subway, subaquatic, subterranean, subzero, subculture, suboptimal, subordinate, subservient