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Suffix · forms adjectives

-acious / -icious

From Latin "-ax/-acis": means "full of" or "having the quality of" to a high degree. Tenacious, audacious, malicious, delicious.

In Spanish: -az / -ioso / -osoLiterary

Written by Bryan López, English teacher · Updated August 2026

What this suffix does

The suffixes -acious and -icious are variants of the same Latin origin "-ax/-acis" (having the quality of, to an intense degree). They attach to Latin roots to create adjectives describing a quality at a dominant or elevated level. -acious: tenacious, audacious, vivacious, loquacious, voracious, sagacious, rapacious. -icious: malicious, suspicious, delicious, ambitious, vicious, auspicious, propitious. Spanish equivalents vary: -az (tenaz, voraz, locuaz), -ioso (malicioso, ambicioso), -oso (delicioso, sospechoso).

The most frequent and their register

High frequency (B2-C1): delicious = full of delight (del + icious) suspicious = generating or having suspicion malicious = with deliberate harmful intent ambitious = driven by strong ambition vicious = fierce, violent, cruel More literary register (C1-C2): tenacious = holding firmly, not giving up audacious = daringly bold (can be admirable or scandalous) vivacious = full of energy and liveliness loquacious = talking a great deal voracious = devouring, literal or figurative ("a voracious reader") sagacious = shrewd, perceptive rapacious = aggressively greedy

Figurative uses: "voracious reader" and others

Many of these words have elegant figurative uses: "a voracious reader" = someone who devours books (voracious literally = eating greedily; figuratively = consuming something intensely) "a tenacious campaigner" = an activist who does not give up. "an audacious plan" = a daringly bold plan. "a vivacious personality" = a lively, animated personality. In academic and journalistic texts at advanced level, these words appear frequently — their precise use distinguishes a B2 from a C2 writer.

How it is formed

Latin root + acious (group A) or + icious (group B). The variant cannot be predicted: learn word by word.

  • root + acious (intense quality, often positive or neutral)
    ten (hold) = tenaciousaud (dare) = audaciousviv (live) = vivaciousloqu (speak) = loquaciousvor (devour) = voracious
  • root + icious (quality, often moral)
    mal (bad) = malicioussus (under) = suspiciousdel (delight) = deliciousambit = ambitiousvic (vice) = vicious
  • root + acious/icious → noun in -acity/-icity
    tenacious → tenacityaudacious → audacityvoracious → voracitymalicious → malicesuspicious → suspicion

The two forms -acious and -icious are historically the same Latin ending at different stages of evolution into English. There is no rule to predict which to use: memorise by word. The corresponding noun usually ends in -acity, -icity or -ice.

How it is pronounced

-acious / -icious/eɪʃəs/ or /ɪʃəs/ · sounds like 'AY-shus' or 'IH-shus'

Tap the button to hear how the ending sounds. Each word in the table has its own audio.

Examples

Base word
With -acious / -icious
In a phrase
  • ten (hold)tenaciousShe's tenacious. She never gives up, no matter how hard things get.
  • aud (dare)audaciousIt was an audacious move, but it actually worked.
  • viv (live)vivaciousMy aunt is so vivacious, she lights up every room she walks into.
  • vor (devour)voraciousHe's a voracious reader. He finishes a book every week.
  • loqu (speak)loquaciousOur tour guide was very loquacious. He talked the whole trip.
  • mal (bad)maliciousSomeone left a malicious comment on her photo, so she deleted it.
  • sus (under)suspiciousThe neighbors got suspicious when they saw a strange car parked outside.
  • del (delight)deliciousThis cake is delicious. Can I have another piece?
  • vic (vice)viciousBe careful, that dog can be vicious with strangers.
  • sag (perceive)sagaciousHer grandfather was a sagacious old man who always gave good advice.

Common mistakes

confusing "suspicious" and "malicious"
"suspicious" = generating or harbouring suspicion; "malicious" = having deliberate harmful intent

"suspicious" can apply to someone who suspects ("I am suspicious of him") or to what arouses suspicion ("suspicious behaviour"). "malicious" implies intent to harm: "a malicious lie" = a lie told with intent to hurt.

"vicious" = addicted to vices
"vicious" = fierce, violent, cruel, or a vicious circle

In modern English "vicious" primarily means fierce, violent or cruel: "a vicious attack", "a vicious dog". Also: "vicious cycle/circle" = círculo vicioso. Not primarily used for addictions.

audacious = always positive
audacious = daringly bold in a way that can be impressive or shocking

"audacious" can be a compliment ("an audacious creative vision") or a rebuke ("the audacity of the claim"). The boldness it implies can be admired or censured depending on context.

A trick to remember it

-acious/-icious = "having the quality of" to a high degree. Group A (-acious): tenacious, audacious, vivacious, voracious, loquacious. Group B (-icious): malicious, suspicious, delicious, vicious, ambitious. Elegant literary use: "a voracious reader", "tenacious spirit", "audacious vision".

Practise what you learned

Exercise 1 · Form the word

"A ___ reader" = someone who devours books: vor___

Hint: vor + acious = ?

Exercise 2 · Pick the right one

What is the difference between "suspicious" and "malicious"?

Exercise 3 · Pick the right one

"Tenacious" describes someone who...

Frequently asked questions

What does the suffix -acious / -icious mean in English?

The suffix -acious / -icious from Latin "-ax/-acis": means "full of" or "having the quality of" to a high degree. Tenacious, audacious, malicious, delicious. In Spanish it usually maps to -az / -ioso / -oso.

How do you pronounce -acious / -icious?

The ending -acious / -icious is pronounced /eɪʃəs/ or /ɪʃəs/ · sounds like 'AY-shus' or 'IH-shus'. For example, "tenacious".

Can you give an example of a word with -acious / -icious?

"ten (hold)" becomes "tenacious". It is a typical example of the -acious / -icious suffix.

Other useful suffixes

  • -esque

    From Italian "-esco": means "in the style of" or "reminiscent of". Kafkaesque, picturesque, grotesque.

  • -itude

    From Latin "-itudo": forms abstract nouns of state or quality. Solitude, gratitude, magnitude, fortitude.

  • -ous / -ious

    Turns a noun into an adjective meaning "full of" or "having that quality": danger becomes dangerous.

Learn every English suffix

-tion, -ness, -ful, -ly, -able... every ending you need to understand thousands of words at once.

View all suffixes
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