abhedo hyekarūpatvaṃ nīrūpeṣu ca tat kutaḥ / ekatve 'rthasya paryāyāḥ prāpnuvanti ca vācakāḥ //
"Non-difference" means having the same form; how can this [sameness of form] exist in formless things? Words become synonymous only when their referent is one [and the same].