Can anyone tell me which noun should I use for absorbing; is it absorbtion or absorption?

I read some articles in which (in my opinion) both words were used interchangeably. Or maybe it was a typo.


2 Answers 2


Absorption is the correct spelling. Absorbtion is a very common misspelling.

Considering it's absorb, absorbance, and a whole family that takes b, while Absorption is quite alone with its p the prevalence of the misspelling is not surprising really.


The correct one is, as SF says, absorption, not absorbtion.

Absorb has a B but when the suffix -tion is appended to it, the second B changes to P. So why does it happen?

Why is absorption spelt with a P

Human vocal tract is designed in such a way that consonant clusters that differ in voice are difficult to pronounce, because changing from voiced to voiceless consonant requires independent movement of the larynx, which can be difficult to switch on and off during normal speech.

There's a process called Assimilation which makes nearby sounds more similar. There are three main types of assimilation; assimilation of place, voicing assimilation and assimilation of manner.

  • In assimilation of place, the place of articulation of one of the two adjacent sounds is changed. For example, ten bikes is often pronounced tembikes (the place of articulation of n changes from alveolar to bilabial)
  • In voicing assimilation, one of the two adjacent sounds changes its voicing. For example, have to is often pronounced hafta in normal speech (the place of articulation of v is the same, but the voicing changes).
  • In assimilation of manner, the manner of articulation of one of the two adjacent sounds changes and becomes more like the other. Example: the word assimilation itself is an example of this type of assimlation. The prefix was ad- which became as- in anticipation of the following /s/ (i.e. the place of articulation of both /d/ and /s/ is the same, but the manner of /d/ changed from plosive to fricative)

Absorption is an example of Voicing assimilation. This assimilation had already occurred in Latin before the word entered English.

We could say, the final sound of absorb is voiced bilabial plosive, it became voiceless bilabial plosive in anticipation of the following voiceless sound of the suffix -tion (i.e. /ʃ/).

Other examples include:

  • describe → description,
  • prescribe → prescription
  • subscribe → subscription etc.

Voicing assimilation is very common, for instance, the plural marker -s becomes /z/ when the preceding sound is voiced, and the past tense marker -ed is pronounced /t/ when the preceding sound is voiceless

  • Bag + s → bags, the s is pronounced /z/ because the preceding /g/ is voiced
  • Pass + ed → passed - the ed is pronounced /t/ because the preceding /s/ devoices the following consonant /d/.

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