brotherliness (n.)

Middle English brotherli, "between brothers," from Old English broðorlic "of or pertaining to a brother;" see brother + -ly (1). The meaning "fraternal, kind, affectionate" is from 1530s.

word-forming element denoting action, quality, or state, attached to an adjective or past participle to form an abstract noun, from Old English -nes(s), from Proto-Germanic *in-assu- (cognates: Old Saxon -nissi, Middle Dutch -nisse, Dutch -nis, Old High German -nissa, German -nis, Gothic -inassus), from *-in-, originally belonging to the noun stem, + *-assu-, abstract noun suffix, probably from the same root as Latin -tudo (see -tude).