Generally, a colleague would be someone who is employed by the same employer as you, though possibly in a completely different role. You could also call this person a 'fellow employee.' A co-worker, however, is normally someone working in the same company and also in a similar role to yourself. Another name for such person is 'workmate.'
An 'associate' is someone who you are associated with at work, possibly in a higher or lower position than yourself.
I asked my co-worker to takeover for me when I was away for vacation.
Your colleague/coworker/associate/fellow employee, they all mean basically the same thing; people who work in your workplace and have a similar ranking as you. Maybe one difference is that your co-worker might be someone that you work with directly. However, they are mostly used interchangeably.
A colleague = one member of a group of people you work with (pronounced as 'ka-lig')
Co-worker = someone you work with, especially if they are at the same level as you or if they do a similar job as you
Workmate = a person you work with (mate = partner or friend)
A fellow worker = a FELLOW is someone who has the same job, interests or does a similar activity as you...example = fellow player, fellow soldier, fellow student, etc.
An associate = someone you are closely connected with such as a business partner, a friend, etc
A partner, co-partner, collaborator are also used, depending on the situation.
A fellow worker （同僚）
= a FELLOWは、自分と同じ仕事、
趣味、活動をしている人です。
例fellow player, fellow soldier, fellow student等
An associate（同僚）
= ビジネスパートナーや友人のように
密接に関係がある人
状況によっては
A partner, co-partner, collaborator も使う
ことができます。
"colleague" and "co-worker" mean the same thing. It’s all about preference, some people prefer to say one over the other. "colleague" also sounds a bit more formal.
日本語の「同僚」は「coworker」「colleague」などと訳されます。
この二つについて明確な違いを挙げるのは難しいです。
人によっても定義が異なるかもしれません。
すごくざっくり言うと、「colleague」よりも「coworker」の方がカジュアルな言葉です。
そこから先は意見の分かれる領域だと思います。
【例】
We work at the same company.
→私たちは同じ会社で働いています（職場の同僚です）。
ご質問ありがとうございました。
Both of these words are similar and can be used to describe someone you work with. However, you
can also use colleague to describe a fellow student or someone else you may study or spend time
with. Although it is a formal word.
Colleague - One of a group of people that work together.
Coworker - a person with whom one works, typically someone in a similar role or at a similar level.
Teammate- A member of a team.
Colleague / Coworker / Teammate are all used interchangeably, and they have very similar meanings.
Colleague usually means that you work for the same employer, for example, the same company.
Coworker usually means someone that works in the same company in a similar role or position.
A Teammate is member of a team belonging to the same. Teammates can be either coworkers or
colleagues.
Examples:-
1. Mr. John and Mr. Smith are colleagues, they both work for Next Generation Company, however, mr. John is a Supervisor, and Mr. Smith is an entry level employee.
2. Ms. Sue and Ms. Maria are both co-workers, they both work in the Sales department as Sales
Agents.
Colleague、Coworker、Teammateはすべて同じように使用され、とても似た意味を持っています。
Colleagueは通常、同じ雇用者の元（例えば、同じ会社）で働いている人を意味します。
Coworkerとは通常、同様の役職にいる同じ会社で働く人のことです。
Teammateは、同じチームに属するメンバーです。Teammatesは、coworkersやcolleaguesであることがあります。
【例文】
1. Mr. John and Mr. Smith are colleagues, they both work for Next Generation Company, however, mr. John is a Supervisor, and Mr. Smith is an entry level employee.（JohnさんとSmithさんは同僚で、2人ともNext Generation社に勤めています。ただし、Johnさんはスーパーバイザーで、Smithさんは新入社員です）
2. Ms. Sue and Ms. Maria are both co-workers, they both work in the Sales department as Sales Agents.（SueさんとMariaさんは同僚です。2人とも営業職として営業部で働いています）
Both of these words are similar and can be used to describe someone you work with. However, you can also use colleague to describe a fellow student or someone else you may study or spend time with socially.
同僚は colleague / coworker (co-worker) と言います。
どちらを使うかは個人の好みだと思います。
違いを説明している先生もいるので、もちろん参考にしてください。
いくつか例文を挙げておきます。
A: Do you get along with your co-workers?
B: Yes. We are all friends.
A: 同僚とうまくやってる？
B: うん。みんな友達だし
He only has one coworker.
彼の同僚は一人しかいない。
His colleague is a very famous professor of literature.
彼の同僚は文学の分野ではとても有名な教授です。
「同僚」は英語で「colleague」と言います。「coworker」や「workmate」などの言い方も使われています。「colleague」という言い方の方が「フォーマル」なニュアンスを与えます。「coworker」はイギリス英語であまり使われていません。イギリス人は「coworker」よりも「workmate」という言い方を使います。
I get on well with my colleagues.
（私は同僚と仲が良い。）
I hate my coworkers. They are always talking loudly when I’m trying to work.
（私は同僚が嫌い。私が仕事をしようとしている時に彼らはうるさくしゃべっている。）
I went to the pub with my workmates on Friday evening.
（金曜日の夜に同僚と一緒にパブに行った。）
同僚は英語でcolleague又はco-workerと言います。
Colleagueもco-workerも仲間というニュアンスがありますがColleagueはco-workerよりそういうニュアンスが強いです。
例）
彼女は同僚と上手くいけないね
She can't manage to get along with her co-workers
私の同僚は皆すごく真面目
My colleagues are all very dedicated
私の同僚は来月産休に入ります
My co-worker is going on maternity leave next month
ご参考になれば幸いです。
「同僚」は英語で colleague や co-worker と言います。
He is one of my colleagues.
彼は私の同僚のひとりです。
My co-workers are all American.
私の同僚はみんなアメリカ人です。
まとめて team ということもあります。
Our team has been working on this project for a month.
私たちのチームは、このプロジェクトに1ヶ月取り組んでいます。
参考になれば幸いです。
イギリス 
アメリカ合衆国 
ニュージーランド 
日本 
カナダ 
