subservient, a. subordinate, [subject], [inferior]; serviceable, conducive.
subside, v. [decrease], [sink], [abate], [fall].
subsidence, n. [decrease], [abatement].
substantiate, v. [verify], corroborate, [confirm], [prove].
substantiation, n. corroboration, [confirmation], [verification].
substitute, v. [exchange], commute.
substitute, n. deputy, proxy, [representative], [agent], lieutenant, [delegate], [vicar], envoy, locum tenens; [makeshift], expedient, [shift], [resource]. Associated word: vicarious.
substitution, n. [exchange], commutation.
subterfuge, n. [artifice], [evasion], [shift], [sophistry], [excuse].
subtile, a. [rare], [fine], ethereal, [delicate]; [crafty], [artful].