In ancient times, there was the practice of burying people alive with the dead.
Tips
usage
殉 is a bound morpheme. Common compounds: 殉职 (die in the line of duty), 殉国 (die for one's country), 殉情 (die for love), 殉葬 (burial sacrifice), 殉道 (martyrdom).
Death radical on the left — pictograph of cracked bones — marks 殉 as a death-related verb. To die for a cause, or in ancient times to be buried alongside one's lord. Same radical drives 死 (die), 殊 (kill/special), 残 (cruel/remnant), 殡 (funeral).
旬 supplies the sound — xún → xùn — through a tone shift only. The same 旬 phonetic drives 殉's near-cousin 询 (xún, inquire) and 询's tonal partner 殉. Mnemonic: ancient martyrs were memorialized in mourning rites lasting one cycle 旬 of ten days.