Of, characteristic of, or befitting sisters or a sister. (adjective)
As a sister. (adverb)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Use "sisterly" in a sentence
"But there was nothing "sisterly" about the message, which urged Sor Juana to giveup writing and devote herself entirely to religion."
"As a subordinated sex-class, women on The Farm could have brought forth the Mighty Mouse response Stephen desired only if they had forged a more thoroughgoing feminist consciousness, the kind of sisterly, but oppositional solidarity that enabled women at Black Bear Ranch to, in the words of one male resident there, "bust the male work ethic" and negotiate a more equitable sexual division of labor."
"However, my younger sister is 18 years younger than me and I hope that when she's slightly older we'll have the kind of sisterly relationship described above."