shelteryoudaoicibaDictYouDict[shelter 词源字典]
shelter: [16] The origins of shelter are unclear, but the most usually accepted explanation is that it is an alteration of the now obsolete sheltron. This denoted a body of troops which protected itself in battle with a covering of joined shields. It was descended from Old English scieldtruma, a compound formed from scield, the ancestor of modern English shield, and truma ‘troop’.
=> shield[shelter etymology, shelter origin, 英语词源]
shelter (n.)youdaoicibaDictYouDict
1580s, "structure affording protection," possibly an alteration of Middle English sheltron, sheldtrume "roof or wall formed by locked shields," from Old English scyldtruma, from scield "shield" (see shield (n.)) + truma "troop," related to Old English trum "firm, strong" (see trim).

If so, the original notion is of a compact body of men protected by interlocking shields. OED finds this "untenable" and proposed derivation from shield + -ture. Figurative sense is recorded from 1580s; meaning "temporary lodging for homeless poor" is first recorded 1890 in Salvation Army jargon; sense of "temporary home for animals" is from 1971. Related: Shelterless.
shelter (v.)youdaoicibaDictYouDict
1580s, "to screen, protect," from shelter (n.); in the income investment sense, from 1955. Meaning "to take shelter" is from c. 1600. Related: Sheltered; sheltering.