One Step Now Education

August 7, 2026

indefatigable

This is one of those words that looks like it's chock full of affixes. So much so that I'm not even sure where the base is. I have two possibilities I'm looking at based on previous investigations.

Before we're done, we will look at adjectives and their functions, including as a subject complement. We will also take a closer look at the suffix <-able> and how it can be confusing if you're consulting a resource list from the internet. They often talk about suffixes and meaning when that's not quite the right way to think about it. Those same lists can get you in trouble with intensive prefixes as well. After this investigation, you will have reasons to push back on some of these lists. Finally, we'll swing back around to a grapheme we discussed last week and how it can help us understand grapheme functions.

Meaning

What is this word's meaning and how does the word function?

I might start by showing a student the following sentences:

• The indefatigable scientist ran experiment after experiment until she finally found the answer.
• The rescue team was indefatigable, searching for the missing hiker through the rain and cold.
• Her teammates were bent over, gasping for air, but Maya, indefatigable, sprinted down the court calling for the ball.

Then I'll ask, "After reading these three sentences, what would you say indefatigable means?" We might read the sentences together if I think there will be issues.

I make sure that in all three sentences, the word occurs in different contexts. The first sentence takes place in a lab, the second sentence takes place outdoors, and the third sentence takes place on the basketball court. I don't want my student to think that indefatigable occurs in only one situation.

My student may answer, "something like they just keep going." I'd probably nod, as this isn't too far off from the entry in Collins which says it "describes someone who never gets tired of doing something."

I also try to make sure the word is functioning in three different ways. The word class for indefatigable is adjective. Adjectives can function in several ways in text.

An attributive adjective will appear directly before the noun it modifies. In sentence one, the word indefatigable modifies scientist.

An adjective can function as a subject complement, appearing after a linking verb like was in our second sentence.

An adjective can also appear postpositively, or after the noun it modifies, as it does in the third sentence. Some, like English professor Richard Nordquist, would say that indefatigable is operating as an appositive adjective. Like an appositive, which is typically a noun phrase, it is set off by commas in text and occurs directly after the noun it is modifying. Attributive and postpositive are more about the adjective's position in the sentence. In both cases, they are functioning as modifiers.

Structure

What are the elements that make up this word's structure?

There is something structural that helps me know this word is an adjective. See, we may start with Meaning, but Structure can also lead back to Meaning.

indefatig + able

Suffixes don't have a "meaning" of their own, so much as they lend "meaning" to the base, often grammatical information. Here, the suffix tells me this word is an adjective used to describe someone.

The suffix can be thought of as "capable." Someone who is manageable is "capable of being managed." Something that is portable is "capable of being carried," as the base portare.

Contrary to the numerous lists out there, this suffix has nothing to do with the word able. It isn't even related etymologically. Looks can be deceiving and so can some of the resources you find on the internet.

But I suspect there are some other affixes here. On the other end:

in + de + fatig + able

Like suffixes, prefixes don't carry much "meaning" on their own. They are bound and lend meaning to the base they are attached to. With inactive is "not active" and someone who is inconsolable is "not capable of being consoled."

The prefix

Depending on the poster you are looking at, the prefix intensive prefix. Intensive prefixes are prefixes that mean the base has been done thoroughly or completely like in declare, "to be completely clear."

So, let's see what Etymonline says about this prefix, or if it is even a prefix at all.

Our word came to us from Latin via French as so many words do. The entry points us to the Latin defatigare, "tire out," but that verb is derived from the prefix fatigare, "weary." When I remove the infinitive suffix <-are> from that Latin verb, I'm left with

in + de + fatige/ + able

So this word describes someone who is "capable of not being utterly tired."

At this point, I might take it back up to the sentences. Does that adequately describe our scientist in the lab? The rescue team? Maya on the court?

Relatives

What are the word's relatives and history?

Perhaps you spotted the base's connection to another word before I did, fatigue. We can consider this word an etymological relative. It is the French version of the Latin word. We cannot consider it as a candidate for the same matrix as base

At one point, there was defatigable, but some resources suggest it might be a back-formation of our word. There is also infatigable, but it's not common.

Graphemes

What can the pronunciation of the word teach us about the relationship of its graphemes and its phonology?

Graphemes have several functions in words besides spelling pronunciation. When a student spots a "silent" letter in a word, we often try to find out what other function that grapheme has.

So why is the in fatigue? We have several other words from French that follow this pattern: league, prologue, and intrigue are just a few. As with the vanguard last week, the is here to signal that the

That leaves the "also-silent" due and rescue.

Graphemes have many functions, sometimes it's to mark the phonology of another grapheme. Sometimes it's to mark a convention of English orthography.

Next Steps

What concepts from this investigation can we explore next to learn more about the English orthographic system?

Sometimes these investigations can be thoroughly exhausting. As I've said many times before, I don't go into all this detail with my students. I only go this deep so that you can learn more about the English orthographic system. After all, the more you know about the English orthographic system, the more indefatigable you will become when studying any word with students.

Stay curious,

Brad

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PS. I have a sort for the prefix

PPS. The fact that suffix <-able> isn't related to able and suffix <-ability> isn't related to ability reminds me that suffix <-less> is also not related etymologically to the word less.