Synonyms for fellow

Most common

1. Chap — A male person; a bloke, a chap, a guy, a man; also, preceded by a modifying word, sometimes with a sense of…

man, buddy, guy informal, person, human being, boy, gent, lad, geezer, feller, dog, cuss informal US, blighter, chap slang dated UK, bloke slang informal UK AU IE, dude slang, fella slang, cat slang dated, bird slang, birdy CA, punk slang dated, covey dated UK, cove dated UK

2. Colleague — A companion; a comrade

3. Friend

friend, boy-friend, beau, swain

4. Comrade

comrade, familiar, companion dated

Other

n. 1
A companion; a comrade.
n. 2
A male person; a bloke, a chap, a guy, a man; also, preceded by a modifying word, sometimes with a sense of mild reproach: used as a familiar term of address to a man.
n. 3
An animal which is a member of a breed or species, or a flock, herd, etc.
n. 4
An object which is associated with another object; especially, as part of a set.

Word family: fella feller fellowship
Phrases: fellow feeling fellow citizen fellow traveller fellow man old fellow shallow fellow visiting fellow fellow traveler

or Fellow?

Fellow has almost gone out of use in this connection, except in an inferior or patronizing sense.

J. C. Fernald, English Synonyms and Antonyms (1914)

Use in printed books, per decade from 1850 to 2019.

3 letters: man¹, guy¹, boy¹, dog¹, cat¹, lad¹
4 letters: dude¹, bird¹, mate¹, punk¹, peer¹, chap¹, cove¹, beau¹, gent¹, cuss¹
5 letters: match¹, equal², buddy², tally², bloke¹, fella², swain¹, birdy², covey²
6 letters: person², friend¹, member², buster², cohort², geezer, feller²
7 letters: partner², comrade², adjunct², compeer
8 letters: familiar³, neighbor², blighter, confrere²
9 letters: associate⁴, companion³, colleague², neighbour², attendant³
10 letters: workfellow, consociate
11 letters: counterpart³

The small number after each word is its number of syllables (equal² = 2 syllables).