Etymology: Old English insegel = Old Frisian insigel, -il (Middle Dutch inzēgel), Old High German insigili (Middle High German insigele, -gil, German insiegel), Old Norse innsigli (Danish indsegl), all strong neuter. Compare also (without in-) Gothic sigljo weak neuter, Middle High German sigel, German siegel, Middle Dutch zeghel, Dutch zegel. The stem of the word evidently represents Latin sigillum ‘little sign, figure, or token, seal’ (diminutive of Latin signum ‘sign, mark, token’), whence Old French seel , English seal n.¹; but the origin of the prefix in- in the Germanic forms is obscure, since no late or medieval Latin insigillum appears. Franck ( Etym. Woorden-bk. Nederl. T. s.v. Zegel) suggests that it may have been taken over in some way from Latin insigne ‘mark, sign’, used also in medieval Latin in sense ‘seal’. In the verb, the prefix raises less difficulty; a medieval Latin insigillare actually occurs (though sometimes as a rendering of Old English inseglian ), and enseeler is common in Old French (see enseal v.).

Etymology: Old English inseglian = Old High German insigilen , Old Norse innsigla ; medieval Latin insigillāre (Du Cange): see inseil n.