investigational

adj

By · According to Wiktionary data (CC BY-SA) ·

"investigational" is a 15-letter English headword indexed on PlainSpell.

The verdict

“investigational” is uncommon English (frequency #50,009 among 2,140 “I” headwords), classed as an adjective. The kind of spelling people second-guess.

#50,009
frequency rank, English
2,140
“I” headwords

According to Wiktionary data (CC BY-SA, analyzed September 3, 2026) - Of, or relating to investigating, or to an investigation.

Corpus desk

Index EN-investigational · investigational · English

investigational · rank #50,009 · 0 variants · 0 confusables

  • FREQ-RARE #50,009
  • LEN-MEGA 15 letters
  • VOW-7 7 vowels
  • CONFUS-0 No pairs
  • VAR-0 0 variants
  • BOOK-MID 2,140
  • PHOTO-FINISH intravenously

Nearest frequency peer: intravenously (-1 rank slots)

Read with this headword: Spelling guide for this pattern

Desk codes from Wiktionary headword shape, FrequencyWords rank tier, confusable-pair count, generated misspelling depth, letter-cohort book size, and photo-finish peer. Not a difficulty grade.

Long-tail ranks near “investigational”

Sparse band: bars invert rank so rarer forms read shorter

corpus weight

What this shows Long-tail view: where “investigational” sits against similarly uncommon English ranks.

Source FrequencyWords open word-frequency list As of September 3, 2026
Key facts for investigational
PropertyValue
Headwordinvestigational
LanguageEnglish
Part of speechAdjective
Letters15
Frequency rank#50,009
Misspellings tracked0
Confusable pairs0
SourceWiktionary (kaikki.org)

Long-tail rank of “investigational” in English

Word frequency stretches from the small set of words we reach for constantly (left) out to the long tail barely used once in a while (right).investigationalfalls in this rarity band:

#1#100#1K#10K#100K
← used constantlyrarely used →

The axis is logarithmic, with each marked tick roughly ten times rarer than the last. Rare peers in the same band: “intravenously” (#50,008), “IRI” (#50,010), “interbank” (#50,007). Among 2,140 “I” headwords, “investigational” is #50,009. Source: FrequencyWords open word-frequency list.

Rare enough to double-check

investigational is uncommon English at frequency #50,009 among 2,140 “I” headwords, classed as anadjective. Rarity is why readers land here mid-draft. 2 senses are on record.

Our edit-distance generator produced no likely misspellings for investigational, and the word's spelling is regular enough that our generator found nothing worth flagging. No close-neighbour confusable shows up for this headword in our dataset, which tends to mean the word is visually distinctive enough to stand on its own.

Etymologically, the entry records: From investigation + -al. The correct English form is investigational, spelled I-N-V-E-S-T-I-G-A-T-I-O-N-A-L.

Definition

  1. 1
    Of, or relating to investigating, or to an investigation.
  2. 2
    of, or relating to an unapproved drug or chemical entity being studied.

Recorded use

Wiktionary example

These source excerpts show how investigational appears in context. They illustrate usage; the definition above remains the entry’s reference meaning.

  1. An expanded access protocol allows patients to benefit from an investigational drug prior to FDA approval.

Etymology

From investigation + -al.

Definitions, pronunciation, and etymology for this entry are drawn from Wiktionary via the kaikki.org structured extract (CC BY-SA); frequency ordering uses the FrequencyWords open word-frequency list (2018 English corpus, MIT). See the methodology for how each field is sourced and updated.

Frequently Asked Questions

How do you spell "investigational"?
"investigational" is spelled I-N-V-E-S-T-I-G-A-T-I-O-N-A-L.
What does "investigational" mean?
As an adjective, "investigational" means: Of, or relating to investigating, or to an investigation.
What is the origin of the word "investigational"?
From investigation + -al. See the full etymology section above for more details.
Is PlainSpell free to use?
Yes, PlainSpell is a completely free word reference. You can look up definitions, pronunciations, confusable pairs, homophones, and spelling corrections across 5 languages without any sign-up or subscription.

Similar English words by spelling shape

Same letter count and similar misspelling depth for "investigational", not the corpus desk frequency band.

Same letter count

Frequency-ranked English headwords with 15 letters (nearest by frequency rank).

instrumentalist#50,006resourcefulness#50,194infrastructural#49,421electrophoresis#49,308

Source: Wiktionary (via kaikki.org) Structured Wiktionary extract

Source: FrequencyWords open word-frequency list