noun

1. Obsolete a person who shares; partner or accomplice
2. a companion; associate
3. a person of the same class or rank; equal; peer
4. either of a pair of corresponding things; mate
5. a graduate student who holds a fellowship in a university or college
6. a member of a learned society
7. at some British and U.S. universities,
   1. a faculty member who is a member of the governing body
   2. a scholar, journalist, etc. who is appointed on a fellowship for a given period of research, teaching, or both
8. Obsolete
   1. a person of a lower social class
   2. a coarse, rough man
9. Informal
   1. a man or boy: often in familiar address
   2. a person; one a fellow must eat
10. Informal a suitor; beau

Etymology: ME felaghe < Late OE feolaga, partner < feoh (see fee) + laga, a laying down (see law), after ON félagi: basic sense, “one laying down wealth for a joint undertaking”; fellowsenses , , , after L socius: see associate

adjective

1. having the same ideas, position, work, etc.
2. in the same condition; associated fellow workers