Definition of "thicken"

thicken

/ˈθɪkən/

verb
third-person singular simple present thickens, present participle thickening, simple past and past participle thickened
1. (transitive) To make thicker (in the sense of wider).
2. (transitive) To make thicker (in the sense of more viscous).
3. (intransitive) To become thicker (in the sense of wider).
  Quotations
  As we age, the major arteries of our bodies frequently become thickened with plaque, a fatty material with an oatmeal-like consistency that builds up along the inner lining of blood vessels. The reason plaque forms isn’t entirely known, but it seems to be related to high levels of cholesterol inducing an inflammatory response, which can also attract and trap more cellular debris over time.
  2013 July-August, Stephen P. Lownie, David M. Pelz, “Stents to Prevent Stroke”, in American Scientist
4. (intransitive) To become thicker (in the sense of more viscous).
5. (transitive) To strengthen; to confirm.
  Quotations
  And this may helpe to thicken other proofes,/ That do demonstrate thinly.
  c. 1603–1604 (date written), William Shakespeare, “The Tragedie of Othello, the Moore of Venice”, in Mr. William Shakespeares Comedies, Histories, & Tragedies […] (First Folio), London: […] Isaac Iaggard, and Ed[ward] Blount, published 1623, [Act III, scene iii]
6. (transitive) To make more frequent.