Old English swellan "grow or make bigger" (past tense sweall, past participle swollen), from Proto-Germanic *swellanan (source also of Old Saxon swellan, Old Norse svella, Old Frisian swella, Middle Dutch swellen, Dutch zwellen, Old High German swellan, German schwellen), which is of unknown origin, perhaps a substratum word. Of emotions from late 14c., of music from 1749. Related: swelled; swollen; swelling.
"swelled, marked by swelling in any sense," early 14c., past-participle adjective from strong conjugation of swell (v.); from Old English geswollen, past participle of swellan. More commonly used than swelled.