Brotherly

wiktionary

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From Middle English brotherly, from Old English brōþorlīċ, from Proto-Germanic *brōþurlīkaz, equivalent to brother +‎ -ly. Cognate with Dutch broederlijk(“brotherly”), German brüderlich(“brotherly”), Swedish broderlig(“brotherly”).

etymonline

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brotherly (adj.)

Old English broðorlic "of or pertaining to a brother;" see brother + -ly (1). Meaning "fraternal, kind, affectionate" is from 1530s.