Not always.

Why do you need help figuring this out?

My understanding of the usage of the the term Freethinker, in the context of theism/deism, is describing a person not restricted to question religious (belief in my god/gods) dogma (conviction of faith (belief without evidence). For example, the term "Death to the infidel!" imposes a standard that does not allow members of that faith to be free to think beyond the teachings of their religion.

i.e. theists/deists are NOT FREE to think (question) their beliefs.

The words are not synonymous, not even close, they don't even reference similar notions.

Freethinker is a broader term which can, but doesn't necessarily, encompass deists. Freethinking can apply to any area of life, while deism applies only to the area of religion and god(s). One could even validly argue that many deists who dogmatically adhere to a God belief ,be excluded from the umbrella of the term freethinker, at least on that particular point of contention. But one can be freethinking in some areas, and not in others. Freethinker is a highly subjective term, and should be used only loosely.

freethinker

One who has rejected authority and dogma, especially in religious thinking, in favor of rational inquiry and speculation.

The American Heritage® Dictionary of the English Language, Fifth Edition

Free thinking, in my view, is only partial thinking if contained by a group identity. If free is to have it's real meaning a person's thinking ought not be limited in definition by group association. I see a free thinker as someone who can agree at times with people from just about any group; though not always for the same reasons. It is one thing to share a view with a group or association of them on specifics but being 'one of them' immediately removes the freedom part.

Using my own example (don't know any others), I frequently share points of view with believers, Democrats, Republicans, 'Pro-Life and Pro-Choice' groups and even Communists. Belong to those groups? N E V E R

So, for someone to claim to be a free thinker on one hand and identify with a group only means to me that they are free thinking withing the frame of reference for the group but not outside it. I don't evcen identify myself as AN Atheist, but as a-theist; rather describing an attitude or state of mind (adjective) than an identity as part of a group as 'an Atheist'. It isn't splitting hairs because there are plenty of would-be Atheist 'leaders' practicing Popery by setting criteria for what makes a 'real Atheist' or 'better Atheist'.

Many people rejecting gods and such while still clinging to other ideological identities actually call themselves 'free thinkers' solely because of their new atheistic attitude, as though theologies are the only mind enslaving 'isms' on the planet.

Most of what is said below is perfectly good. So I will just add a short funny one.

A deist is someone who rejects belief in religion but not god.
A freethinker is someone who rejects belief in everything except thought.

A freethinker can be a deist but deism was very popular before science as we know it today. Deists believe in a god as creator and that god then hid from us and was not involved in our affairs.

Let's see, a freethinker, as the label says, is someone who thinks freely, as opposed to a paid thinker? A penny for your thoughts! Wow, that salary is fucking low! Now, dentists are people who studied to take care of teeth and get paid way too much for it, oh you said deists, as Seinfeld said, who are these people? Are these people who are in a deis?

In the case of my avatar perhaps, but not true for the great orator and freethinker, Robert Green Ingersoll. Called The Great Agnostic, more people saw him speak than any other 19th century figure.

“When I became convinced that the universe is natural, that all the ghosts and gods are myths, there entered into my brain, into my soul, into every drop of my blood the sense, the feeling, the joy of freedom. The walls of my prison crumbled and fell. The dungeon was flooded with light and all the bolts and bars and manacles became dust.”
Robert Green Ingersoll

The overlap is a member of the empty set.

Overlap maybe a little bit...

Per Google:

Freethinker: a person who rejects accepted opinions, especially those concerning religious belief.

Deist: belief in the existence of a supreme being, specifically of a creator who does not intervene in the universe. The term is used chiefly of an intellectual movement of the 17th and 18th centuries that accepted the existence of a creator on the basis of reason but rejected belief in a supernatural deity who interacts with humankind.

Deists and Freethinkers are overlapping sets.