Wiktionary
n. (context Islam English) A family member who is haram to marry.
Wikipedia
In Islamic sharia legal terminology, a mahram ( Arabic محرم, also transliterated mahrim or maharem) is an unmarriageable kin with whom sexual intercourse would be considered incestuous, a punishable taboo. Current usage of the term covers a wider range of people and mostly deals with hijab and its cultural and regional norms.
The plural form of the word in the Arabic language is maharim with long second vowel (Arabic محارم, also transliterated maharem). Sometimes the word is capitalized but there is not a general consensus that the word should be capitalized like Muslim. (The Arabic alphabet has no upper-case vs. lower-case distinction.)
Being mahram is a mutual condition. If A is mahram to B, B is definitely mahram to A. __TOC__